IGCSE Computer Science Paper 1

These are free worksheets for Paper 1 (Computer Systems) of the Cambridge IGCSE Computer Science syllabus, 0478: topics 1 to 6, covering data representation, data transmission, hardware, software, the internet and its uses, and automated and emerging technologies.

This page lists the 507 modules written for Paper 1, one section per syllabus topic: binary, denary and hexadecimal conversions, binary addition, overflow, logical shifts and two's complement; ASCII and Unicode, sound sampling, image resolution and colour depth; storage units from nibble to exbibyte, file size calculations and lossy and lossless compression; packets and packet switching, serial and parallel, simplex and duplex transmission, USB, parity, checksums, echo checks, check digits and ARQ; symmetric and asymmetric encryption; the Von Neumann architecture, registers, buses and the fetch-decode-execute cycle; input, output and sensor devices; primary, secondary and virtual memory and cloud storage; MAC and IP addresses and routers; system and application software, operating system functions and interrupts; high- and low-level languages, compilers, interpreters and IDEs; URLs, HTTP and HTTPS, DNS, browsers and cookies; digital currency and blockchain; cyber security threats and solutions; and automated systems, robotics and artificial intelligence. Each module includes real practice questions, worked examples and a full answer key.

Each topic has its own journey below, and the larger topics are also split into smaller journeys, so teachers can assign a whole topic or one part of it, with progress tracking, class sprints and badges.

Add this whole curriculum to your class, or just the modules your unit needs — Cloodit tracks who's stuck automatically.

Add to class →

1.1 Number Systems (27 modules)

Number bases: denary, binary and hexadecimal How many different digits a number system uses: denary is base 10 (digits 0-9), binary is base 2 (digits 0-1) and hexadecimal is base 16 (digits 0-9 and A-F).

Denary place values Each denary column is worth 10 times the column to its right (1, 10, 100, 1000). A number is the sum of each digit times its column value, e.g. 345 = 300 + 40 + 5.

16-bit binary place values The 16 place values of a 16-bit binary number. Each is double the one on its right, and the right-hand byte uses 128 to 1. All 16 bits set to 1 make the largest value, 65535.

Converting 16-bit binary to denary To convert 16-bit binary to denary, write the place values (32768 down to 1) over the bits, skip the 0 columns, then add the values that have a 1 under them. Leading zeros add nothing.

Converting a denary number to 16-bit binary Work from 32768 down to 1. Write 1 and subtract if the place value fits in the remainder, otherwise write 0. Keep leading zeros so the answer has 16 digits.

Hexadecimal digits 0 to 9 and A to F The 16 hex digits: 0-9, then A=10, B=11, C=12, D=13, E=14, F=15. Each digit stands for one 4-bit value, and F (15) is the largest single hex digit.

Hexadecimal place values Hex place values, left to right. Each column is worth 16 times the column to its right. Two hex digits cover 0 to 255 and four hex digits cover 0 to 65535.

Converting hexadecimal to denary Multiply each hex digit's value (A-F = 10-15) by its column value (1, 16, 256, 4096), then add the results. Example: 2F = 2 x 16 + 15 = 47.

Converting denary to hexadecimal Divide the denary number by 16 again and again. Read the remainders from last to first, writing 10 to 15 as A to F. Check by converting the hex back to denary.

Converting binary to hexadecimal using nibbles Split the bits into groups of four from the right (nibbles), pad the left group with zeros if needed, then replace each nibble with its hex digit.

Converting hexadecimal to binary using nibbles Hex to binary: replace each hex digit with its 4-bit nibble, keeping leading zeros, then join the groups. A is 1010 and 3 is 0011, so A3 is 10100011.

Why hexadecimal is used instead of binary A base-16 system that shortens binary. One hex digit stands for four bits, so values are shorter to read, easier to copy without mistakes and quick to convert to and from binary.

Where hexadecimal is used in computer science Base-16 notation that shortens binary so people can read and write it. Used in colour codes, MAC addresses, memory addresses and error codes.

Binary addition rules Binary addition rules: 0+0=0, 0+1=1, 1+1=10 (write 0, carry 1) and 1+1+1=11 (write 1, carry 1). Add column by column, carrying into the next column.

Adding two 8-bit binary integers Add two 8-bit binary numbers column by column from the right. Carry any 1 to the next column on the left. 1 + 1 = 10, so write 0 and carry 1. Check by adding the denary values.

Overflow in an 8-bit register An error when an 8-bit addition gives a result over 255. It needs a 9th bit, so the carry out of the leftmost column is lost and the stored result is wrong.

Logical left shift Moves every bit one place left. The leftmost bit falls off and is lost, and a 0 fills the empty place on the right. In 8 bits, 00000101 becomes 00001010.

Logical right shift Moves every bit one place right. The bit at the right end is lost and a 0 fills the empty left end. For a positive integer this halves the value (rounded down).

Multiple shifts Shifting by n places moves every bit n positions, losing n bits at one end and adding n zeros at the other. Shift all 8 bits out and you get 00000000.

Shifts as multiplying and dividing by powers of 2 Each left shift multiplies a binary number by 2 and each right shift divides it by 2, so n shifts multiply or divide by 2^n. Bits shifted off the end are lost.

Why two's complement is used A way to store negative integers in binary. The leftmost bit shows the sign: 0 means positive, 1 means negative. Positive numbers look the same as ordinary binary.

The sign bit worth -128 The 8-bit two's complement place values. The leftmost bit (the sign bit) is worth -128 when it is 1, and the other seven bits keep their usual values, so 10000000 = -128.

Range of 8-bit two's complement The range of an 8-bit two's complement integer: 10000000 is -128, 11111111 is -1 and 01111111 is 127. Unsigned 8-bit binary gives 0 to 255 instead.

Converting 8-bit two's complement to denary Add the place values with a 1 under them to get the denary value. A leftmost 1 means -128 is added: 11110110 = -128+64+32+16+4+2 = -10. A leftmost 0 means positive.

Converting a positive denary number to two's complement A denary number from 0 to 127 is written as ordinary binary, padded with zeros to 8 bits so the leftmost sign bit is 0. Numbers above 127 cannot be stored.

Converting a negative denary number to two's complement Write the positive value in 8-bit binary, flip every bit, then add 1. Example: 5 is 00000101, flip to 11111010, add 1 to get 11111011 (-5).

Checking a two's complement conversion Check a two's complement answer by converting it back to denary with these place values, then compare the result with your starting number. They must match.

Just this content description: the 1.1 Number Systems journey · Add 1.1 Number Systems to a class →

1.2 Text, Sound and Images (12 modules)

Character set The agreed list of characters a system can use, with a unique binary code for each one, so every device reads the same code as the same character.

ASCII and its bits per character A character set that gives each character a 7-bit code (128 characters), usually stored in 8 bits. Extended ASCII uses 8 bits for 256 characters.

Encoding a word as 8-bit ASCII binary Look up each letter's ASCII code and write it as an 8-bit binary group, then join the groups in order. Example: A = 65 = 01000001.

Comparing ASCII and Unicode Unicode supports far more characters than 8-bit ASCII but uses 16 or 32 bits per character, so the same text takes up more storage space.

Analogue sound waves and digital sound A sound wave is analogue: its amplitude changes smoothly. A computer stores only separate binary numbers, so the wave a microphone captures must be converted into discrete digital values.

Sample resolution The number of bits used to store each sample of a sound. More bits give more possible volume levels and a more accurate recording. 16 bits per sample is common.

Effect of sample rate and resolution on accuracy and file size Raising the sample rate or sample resolution records the sound more accurately, but it also makes the audio file bigger. Lowering either does the opposite: less accurate, smaller file.

Colour depth The number of bits used to store the colour of each pixel. More bits per pixel means more possible colours, such as 1 bit for 2 colours or 24 bits for true colour.

Number of colours from the colour depth A colour depth of n bits gives 2^n different colours, so each extra bit doubles the number. For example, 2 bits give 4 colours and 8 bits give 256 colours.

Encoding and decoding a small colour image A table giving each colour a binary code. Write each pixel's code row by row to encode an image; read the codes back to redraw it. 4 colours need 2 bits.

Effect of resolution and colour depth on image quality and file size Raising either one improves image quality (sharper detail, smoother colours) but stores more bits, so the file size gets larger.

Choosing settings: quality versus file size Balancing quality against file size: pick the lowest sample rate, resolution or colour depth that still looks or sounds good enough, so the file stays small enough to store or send.

Just this content description: the 1.2 Text, Sound and Images journey · Add 1.2 Text, Sound and Images to a class →

1.3 Data Storage and Compression (30 modules)

Nibble A nibble is a group of 4 bits, so half a byte. Two nibbles make 1 byte. One hexadecimal digit fits exactly in one nibble.

Kibibyte (KiB) A kibibyte (KiB) is a unit of data storage equal to 1024 bytes. The kibi prefix means 1024, and KiB is the first unit above the byte.

Mebibyte (MiB) A unit of data storage equal to 1024 kibibytes (KiB). The mebi prefix means 1024 squared. A typical photo or song is a few MiB in size.

Gibibyte (GiB) A gibibyte (GiB) is a unit of data storage equal to 1024 mebibytes (MiB). A film or memory stick is often a few GiB. The gibi prefix means 1024 cubed bytes.

Tebibyte (TiB) Tebibyte: a unit of data storage equal to 1024 GiB. The tebi prefix means 1024 to the power 4. A typical hard drive might hold 1 or 2 TiB.

Pebibyte (PiB) A pebibyte (PiB) is a unit of data storage equal to 1024 tebibytes (TiB). It is used for very large amounts of data, such as in big data centres.

Exbibyte (EiB) Exbibyte: a unit of data storage equal to 1024 pebibytes (PiB). It is the largest unit in the IGCSE syllabus.

The unit ladder: byte to exbibyte The storage unit ladder from smallest to largest. Above the byte, each unit is 1024 times the one before: 1 KiB = 1024 bytes, 1 MiB = 1024 KiB, and so on up to EiB.

Why storage units use 1024, not 1000 Each storage unit is 1024 times the one before, because computers count in binary and 2 to the power 10 is 1024. So calculations use 1024, not 1000.

Converting bits to bytes and bytes to bits Divide bits by 8 to get bytes. Multiply bytes by 8 to get bits. A nibble is 4 bits, so 2 nibbles make 1 byte. Example: 24 bits / 8 = 3 bytes, and 5 bytes x 8 = 40 bits.

Converting to a larger unit To convert to the next larger unit (bytes to KiB, KiB to MiB, MiB to GiB), divide the size by 1024. The answer may not be a whole number.

Converting to a smaller unit To convert to the next smaller unit (GiB to MiB, MiB to KiB, KiB to bytes), multiply by 1024. The answer should be a bigger number than the one you started with.

Converting across several units To convert across several units, divide by 1024 for each step up the ladder or multiply by 1024 for each step down. Bytes to MiB is two steps, so divide by 1024 twice.

Giving the answer in the unit asked Finish a storage calculation by converting the result into the unit the question asks for, then write that unit with your answer, for example 2 MiB.

Counting the pixels in an image Total pixels = pixels per row times number of rows. For 1920 x 1080 that is 2,073,600 pixels. This is the first step when working out image file size.

Image file size in the unit asked After finding an image size in bytes, divide by 1024 once for KiB, twice for MiB and three times for GiB, to give the answer in the unit the question asks for.

Hertz and kilohertz Sample rate is measured in hertz (Hz), the number of samples per second. 1 kHz is 1000 Hz, so 44.1 kHz is 44100 Hz. Frequency uses 1000, not 1024.

Converting the length of a sound to seconds Sound length must be in seconds before using it in a file size calculation, so multiply minutes by 60 (add any extra seconds). Length is then the third factor in the formula.

Calculating the size of a sound file Uncompressed sound file size in bits is the sample rate (Hz) times the sample resolution (bits) times the length in seconds. Divide the bits by 8 to get bytes.

Sound file size in the unit asked Divide the sound size in bits by 8 to get bytes, then by 1024 to get KiB. Divide by 1024 again to get MiB. Stop at the unit the question asks for.

Checking whether a file fits in the available storage A file fits if its size is less than or equal to the free space. First convert both to the same unit, such as bytes or MiB, then compare the two numbers.

Why compression is needed: less storage space Compressed files are smaller, so they take up less storage space. This means more photos or songs fit on a device, and less storage needs to be bought.

Why compression is needed: less bandwidth A compressed file has fewer bits to send, so it uses less of the shared network bandwidth. This eases congestion and helps video and audio stream smoothly.

Why compression is needed: shorter transmission time The time a file takes to upload, download or send. A smaller compressed file has a shorter transmission time, so downloads, email attachments and web pages are quicker.

Lossy compression permanently removes data Data removed by lossy compression is gone for good, so the original quality cannot be restored. Keep the original file, as re-saving or compressing again only lowers quality further.

Lossy compression of an image by reducing resolution or colour depth Reduces an image's resolution or colour depth to shrink the file. Detail is lost for good. Recalculate width x height x depth to see the saving.

Lossy compression of a sound by reducing sample rate or sample resolution Lowering the sample rate or sample resolution of a sound so it needs fewer bits. The file gets smaller, but the lost sound detail can never be recovered.

Run-length encoding of a row of coloured pixels Run-length encoding of a pixel row stores each run of same-coloured pixels as a count then a colour code, in order along the row. E.g. WWWBB becomes 3W2B.

Decoding run-length encoded image data Repeat each colour code count times along the row to rebuild the pixels, e.g. 3R2B gives RRRBB. Then check the row adds up to the image width.

Comparing lossy and lossless compression Lossy makes smaller files but permanently removes data; lossless keeps all data so the original can be restored, but saves less space.

Just this content description: the 1.3 Data Storage and Compression journey · Add 1.3 Data Storage and Compression to a class →

2.1 Data Transmission Types and Methods (33 modules)

Why data is broken down into packets A small piece of a larger file. Data is split into numbered packets so they share the network and a lost packet can be resent instead of the whole file.

The three parts of a packet The three parts of a packet, in order: the header (start) holds addresses and packet number, the payload (middle) holds the data, the trailer (end) marks the packet's end.

Packet header The first part of a packet. It holds control information: the destination address, the originator's address and the packet number, used to deliver and reassemble the packet.

Destination address in a packet header The address in a packet header of the device the packet must be delivered to. Routers read it to choose where to send the packet. It is usually an IP address.

Originator's address in a packet header The IP address of the device that sent the packet, held in the header so the receiver knows who sent it and can reply or ask for a resend. It differs from the destination address.

Packet number in a packet header A number in the packet header showing the packet's position in the whole message (e.g. packet 3 of 10), so packets that arrive out of order can be put back in the right order.

Packet payload The part of a packet that carries the actual data being sent, such as a piece of a file or message. The header and trailer are not payload.

Packet trailer The last part of a packet. It marks where the packet ends and can hold error checking information, so the receiving device can check the data arrived correctly.

Labelling the structure of a packet A packet has a header (destination address, originator's address, packet number), a payload (the data) and a trailer (marks the end). Label each item by the part it belongs to.

Packet switching Data is split into packets that are sent separately, each routed on its own from router to router, then joined back together in the right order at the destination.

A router controls each packet's route A router reads each packet's destination address in its header and picks the next router to send it to, so every packet's route is decided one step at a time.

Why packets can take different routes Packets from one message can take different routes because each router picks the best available path at that moment, avoiding busy or broken links. Routes may take different lengths of time.

Packets arriving out of order Packets take different routes, so they may reach the destination in a different order from the one sent, e.g. packet 5 before packet 4. Order is not guaranteed.

Reordering packets at the destination After the last packet arrives, the receiving device uses the packet numbers in the headers to put the packets in the right order and joins the payloads to rebuild the message.

Describing the packet switching process step by step Data is split into numbered packets, routers pick each packet's route, packets may arrive out of order, then they are reordered to rebuild the data once the last packet arrives.

Serial transmission Sending data one bit at a time, one after another, down a single wire or channel. The bits arrive in the same order they were sent.

Advantages and disadvantages of serial transmission Sends bits one at a time down one wire: cheaper, no skew and reliable over long distances, but slower than parallel for large amounts of data at the same clock speed.

Parallel transmission Sends several bits at the same time, each down its own wire in the same cable, e.g. 8 bits down 8 wires at once.

Advantages and disadvantages of parallel transmission Sends several bits at once on many wires. Fast over short distances, but needs more wires (higher cost) and is unreliable over long distances because of interference between wires.

Data skew in parallel transmission Bits sent together down parallel wires arrive at slightly different times, so data can be received incorrectly. It gets worse as the cable gets longer.

Comparing serial and parallel transmission Serial sends 1 bit at a time down one wire: cheaper, reliable, better over long distance. Parallel sends many bits at once down several wires: faster over short distances only.

Simplex data transmission Data transmission in one direction only, from sender to receiver, with no reply possible. Example: a keyboard sending key presses to a computer.

Half-duplex data transmission Data can travel in both directions, but only one direction at a time, so devices take turns, like a walkie-talkie.

Full-duplex data transmission Data is sent in both directions at the same time, so both devices can send and receive at once, for example during a telephone call or over a broadband connection.

Advantages and disadvantages of simplex, half-duplex and full-duplex Simplex is one-way only but simple and has no collisions. Half-duplex is two-way by turns, so slower. Full-duplex is two-way at once and fastest, but needs more capacity and costs more.

Choosing a transmission method for a scenario Pick the direction (simplex, half-duplex or full-duplex) and the bit arrangement (serial or parallel), then justify both using the scenario's distance, speed and two-way needs.

What the universal serial bus (USB) is Universal Serial Bus: a standard interface for connecting devices like keyboards, drives and phones to a computer and transferring data between them.

How USB transmits data USB sends data serially, one bit at a time, down a single cable. It works in both directions: half-duplex in older versions, full-duplex in later ones. The cable can also carry power.

USB device detection and drivers When a USB device is plugged in, the computer automatically detects it and loads the driver it needs, so the device works straight away with no need to restart.

USB connectors and cables A USB port and plug of a set shape and wiring, so one cable type connects many different devices to a computer, such as a keyboard, a printer or a phone.

Benefits of USB One standard connector fits many devices, devices are detected automatically, older devices work in newer ports, power comes through the cable, and fast serial transfer is used.

Drawbacks of USB Limits of USB: short maximum cable length (unreliable over distance), slower speed than some interfaces (old ports slow new devices), and a limited number of ports.

Evaluating USB for a given use Judge if USB suits a use by weighing benefits (universal, plug and play) against drawbacks (short cable length, limited speed) for the scenario, such as a printer or drive.

Just this content description: the 2.1 Data Transmission Types and Methods journey · Add 2.1 Data Transmission Types and Methods to a class →

2.2 Methods of Error Detection (39 modules)

Why data is checked after transmission Checking received data, because it can be damaged in transit and the receiver cannot see the original. Spotting the error is the first step to fixing it.

Interference as the cause of transmission errors Unwanted disturbance to a signal, such as electrical noise or crosstalk, that damages data as it travels and can cause bits to be lost, gained or changed.

Data loss When some bits or bytes that were sent never arrive, so the message that is received is shorter than the one that was sent.

Data gain Data gain is when extra bits or bytes that were not sent are added to the data, so the message arrives longer than it was sent. It is a type of transmission error.

Data change Bits arrive altered, such as a 0 flipping to a 1, so the same amount of data arrives but with wrong values. Comparing sent and received bits shows it.

Identifying loss, gain and change in an example Compare the data sent with the data received. Fewer bits or characters means loss, extra ones means gain, and the same length with different values means change.

Error detection versus error correction Checking received data to show that an error has happened. It does not repair the data, so the receiver usually asks for it to be sent again. Some errors can still be missed.

Parity bit One extra bit added to a group of bits (such as 7 data bits) so the total number of 1s follows a rule, even or odd, agreed by sender and receiver. It is used to detect errors.

Even parity A parity bit is added so the total number of 1s in the byte, including the parity bit, is even. Odd count of 1s in the data gives parity bit 1; even count (even 0) gives 0.

Odd parity A rule where the parity bit is set so the total number of 1s in the byte, including the parity bit, is odd. Even number of 1s in the data gives bit 1; odd number gives bit 0.

Working out the parity bit for a byte Count the 1s in the 7 data bits, then set the leftmost parity bit to 0 or 1 so the total number of 1s in the whole 8-bit byte matches the agreed rule (even or odd).

Checking a received byte for a parity error The receiver counts the 1s in the whole received byte, parity bit included. If the count breaks the agreed even or odd rule, an error has occurred and is detected.

What a single parity check cannot detect A single parity check misses an error when an even number of bits change, because the count of 1s keeps the same parity. It also cannot show which bit is wrong.

Parity byte An extra byte sent after a block of data bytes. Each of its bits is the parity bit for one column (bit position) taken down across all the data bytes in the block.

Parity block check Checks a block of bytes in two directions: a parity bit on every byte (row) and a parity byte for the columns, so the wrong row and column pinpoint the error.

Building a parity block with a parity byte Each byte gets a row parity bit, then a final parity byte holds the parity bit for each column. The corner bit is the parity bit of the parity bits, so it checks in both directions.

Finding the error in a parity block In a parity block, the row and the column that both fail their parity check cross at the bit that changed. Flip that bit to correct a single-bit error.

What parity bytes and blocks cannot detect Four flipped bits at the corners of a rectangle keep every row and column parity correct, so a parity block check misses the error. Only one error can be located reliably.

Checksum A value calculated from a block of data by a set rule and sent with it. The receiver repeats the calculation and compares the results. If they differ, an error occurred.

Calculating a checksum Add all the byte values in the block, then keep the remainder after dividing by 256 so the result fits in one byte. Example: 200+100+50=350, 350 mod 256 = 94.

Checking a checksum at the receiver The receiver recalculates the checksum from the received data and compares it with the one sent. Match means no error detected; mismatch means error, so resend is requested.

What a checksum can and cannot detect A sum of the data bytes sent with the data. It catches most changes, losses and gains, but misses swapped bytes or errors that cancel out, and cannot show which byte is wrong.

Echo check The receiver sends a copy of the received data back to the sender, who compares it with the original. A match means no error was detected; a mismatch means the data is sent again.

What an echo check cannot tell you An echo check cannot tell if the error happened on the way there or back, and it can miss errors if both trips are damaged the same way.

Check digit An extra digit added to the end of a number, calculated from its other digits. It is recalculated on entry and compared, to detect data entry mistakes.

Typing errors that a check digit detects An extra digit worked out from the other digits in a number. It catches typing errors: a wrong digit, two digits swapped (transposition), a missing digit or an extra digit.

Calculating a check digit with weights and modulus 11 Multiply each digit by its weight, add them up, divide by 11 and use the remainder (often 11 minus it) as the check digit. A 10 is written X in ISBN-10.

ISBN-13 check digit The last digit of an ISBN-13, found by weighting the first 12 digits 1 and 3 alternately, adding them, and choosing the digit that makes the total a multiple of 10.

Bar code check digit The last digit of a bar code number, worked out from the other digits. The scanner recalculates it and rejects a misread if the digits do not match, so the item must be scanned again.

Checking a number with its check digit on entry Work out the check digit again from the other digits, then compare it with the one entered. If they differ, reject the number and ask the user to re-enter it.

What a check digit cannot detect A wrong number can still pass the check digit test, and a valid number may belong to the wrong item. The check digit tests the digits only, not what they mean.

Automatic repeat query (ARQ) Automatic repeat query: the receiver checks data for errors and replies. If the data is bad or no reply arrives, the sender automatically resends it until it is received correctly.

Positive acknowledgement A message sent by the receiver to tell the sender that data arrived without error. Often written ACK. It is sent only after the error check passes, so the sender can send the next data.

Negative acknowledgement A message (NAK) the receiver sends to the sender when the error check fails, telling it the data arrived with an error so the sender must resend the same data.

Timeout The set time a sender waits for an acknowledgement after sending data. If none arrives in time, it assumes the data was lost and resends it.

The ARQ process step by step Sender sends data and starts a timer. Receiver checks it and replies ACK or NAK. Sender resends on a NAK or a timeout until an ACK arrives.

What ARQ can and cannot do ARQ resends data when a separate check finds an error, so it misses errors that check misses, and a noisy link causes many resends that slow the transfer.

Comparing the error detection methods Parity, parity block, checksum and echo check find errors in transmission; a check digit finds them at data entry; ARQ asks for a resend. Each sends different extra data.

Choosing an error detection method for a scenario Decide if the error happens in transmission or data entry, pick the check that fits, then justify it by what it can and cannot detect.

Just this content description: the 2.2 Methods of Error Detection journey · Add 2.2 Methods of Error Detection to a class →

2.3 Encryption (15 modules)

Interception of data on a network When someone copies data as it travels across a network through routers and other devices, so unprotected data can be read by anyone who intercepts it, for example on public Wi-Fi.

Plaintext The original, readable data (text, file, image or message) before it is encrypted. Decrypting ciphertext with the correct key turns it back into plaintext.

Ciphertext The scrambled, unreadable data made when plaintext is encrypted. It is what gets sent across a network and looks meaningless without the key.

Encryption key A secret value used by the encryption algorithm to scramble data into ciphertext and unscramble it again. A different key gives different ciphertext, and a longer key is harder to guess.

Why encrypted data is useless to an interceptor Encryption cannot stop data being intercepted, but the interceptor sees only ciphertext and cannot get the plaintext without the key, so passwords and bank details stay safe.

Encrypting and decrypting with one shared key The sender encrypts plaintext into ciphertext with a key; the receiver decrypts it back to plaintext using the same key. A wrong key gives unreadable output.

Why a symmetric key must be shared In symmetric encryption, the receiver can only decrypt if they hold the same key as the sender, so the key must be shared before any data is sent.

The risk of sharing a symmetric key If an attacker intercepts a symmetric key while it is being shared, they can decrypt every message that uses that key, so the encryption is defeated.

Public key The half of a key pair that the owner shares openly. Anyone can use it to encrypt data sent to the owner, but it cannot decrypt that data. Only the matching private key can.

Private key The secret half of a key pair. Only the owner keeps it, never sends it, and uses it to decrypt data that was encrypted with their public key.

Encrypting with the recipient's public key To send a secure message, the sender encrypts the plaintext using the receiver's public key, not their own. Only the receiver's private key can decrypt the ciphertext.

Decrypting with the private key Only the recipient's private key can decrypt a message encrypted with their public key. The private key stays secret on the recipient's device, so interceptors cannot read it.

Sending a secure message with asymmetric encryption The receiver shares their public key, the sender encrypts with it, and only the receiver's private key can decrypt it. No secret key is shared, so an interceptor sees only ciphertext.

Choosing symmetric or asymmetric encryption for a scenario Use symmetric if both sides can already share a key safely; use asymmetric for strangers, such as a customer and a website. Justify the choice with 'because'.

Writing an exam answer about encryption A full-mark answer uses the key terms correctly and gives the steps in order: plaintext is encrypted with a key into ciphertext. Encryption does not stop interception.

Just this content description: the 2.3 Encryption journey · Add 2.3 Encryption to a class →

3.1 Computer Architecture (30 modules)

Microprocessor A CPU built as an integrated circuit on a single chip. It is only the processor, not the whole computer, and is found in PCs, phones and embedded devices.

Von Neumann architecture A computer design where instructions and data share the same main memory (RAM) and the CPU fetches them one at a time. This is the stored program concept, named after John von Neumann.

Arithmetic logic unit (ALU) Arithmetic logic unit: the part of the CPU that does calculations (add, subtract) and logic decisions (AND, OR, NOT, comparisons). Results are held in the accumulator.

Control unit (CU) The part of the CPU that decodes instructions and sends control signals to coordinate the ALU, registers, memory and other parts during the fetch-decode-execute cycle.

Registers A very small, very fast storage location inside the CPU (not in RAM) that holds one item of data or one address, such as the PC, MAR, MDR, CIR or ACC.

Program counter (PC) A register in the CPU that holds the address of the next instruction to be fetched. It increments after each fetch and changes when the program jumps.

Memory address register (MAR) Memory Address Register: a CPU register that holds the address of the memory location about to be read from or written to. It holds an address, not data, and sends it along the address bus.

Memory data register (MDR) Memory Data Register: a CPU register that temporarily holds the data or instruction just fetched from RAM, or data about to be written to RAM. It holds data, not addresses.

Current instruction register (CIR) Current Instruction Register: holds the instruction copied from the MDR while the control unit decodes it and the CPU executes it. It stores the instruction itself, not an address.

Accumulator (ACC) A register in the CPU that holds data being worked on and the results of ALU calculations, storing intermediate results before they are saved back to memory or output.

Buses A set of wires that carries data, addresses or control signals between the CPU, RAM and other components. More wires means more bits can be carried at once.

Address bus A one-way bus that carries the address of a memory location from the CPU (sent from the MAR) to RAM. It carries addresses, not data.

Data bus A set of wires that carries data and instructions in both directions between the CPU and RAM. It connects to the MDR.

Control bus A set of wires that carries control signals, such as read and write, from the control unit to other components so they work together. It carries signals, not data or addresses.

The fetch-decode-execute cycle The CPU repeats three stages for every instruction: fetch it from RAM, decode what it means, then execute it. The cycle then starts again with the next instruction.

Fetch: sending the address from the PC to the MAR At the start of fetch, the address held in the PC is copied into the MAR. It then travels along the address bus to RAM. The PC still holds the address at this point, because it is copied, not moved.

Fetch: reading the instruction from RAM into the MDR Fetch step: RAM finds the instruction at the address in the MAR (address bus), a read signal comes via the control bus, and the instruction travels on the data bus into the MDR.

Fetch: incrementing the PC and copying the instruction to the CIR End of fetch: the PC is increased by 1 so it points to the next instruction, and the instruction held in the MDR is copied to the CIR, ready to be decoded.

Decode stage The fetch-decode-execute stage where the control unit reads the instruction in the CIR and works out the operation to perform and the data (operand) it needs.

Execute stage The stage of the fetch-decode-execute cycle where the decoded instruction is carried out, e.g. fetching data, calculating in the ALU, storing in the ACC, or changing the PC.

Tracing one instruction through the registers Recording the contents of the PC, MAR, MDR, CIR and ACC, and the bus used, at each step as one instruction goes through the fetch-decode-execute cycle.

Cache memory A small amount of very fast memory in or near the CPU that stores frequently used instructions and data, so the CPU can get them faster than from RAM.

How cores, cache and clock affect CPU performance How fast a CPU runs programs. More cores, a bigger cache or a faster clock speed can raise it, but each has limits: software must split tasks, cache is costly, and a faster clock makes more heat.

Instruction set The list of all the commands (such as load, add, store and jump) that a CPU design can process. The control unit decodes each instruction using it.

Machine code The binary (0s and 1s) form of instructions that the CPU can run directly. Each instruction has an opcode and an operand. Programs must be translated into it to run.

Embedded system A computer system built into a larger device to perform one dedicated function, usually running a fixed program. Examples: a washing machine controller or a microwave timer.

Devices that use embedded systems A computer built into a device to do one set job, such as in a washing machine, car engine control, alarm, automatic lighting or vending machine.

General-purpose computer A computer, such as a PC or laptop, that can do many different jobs by running different programs, and the user can install new software.

Embedded systems compared with general-purpose computers A computer built into a device to do one dedicated job with a fixed program, unlike a general-purpose computer, which does many different jobs and can run installable software.

Writing exam answers about the CPU A full-mark CPU answer uses exact names for registers, buses and units, and gives the fetch, decode and execute steps in order, e.g. PC to MAR, then MDR, then CIR.

Just this content description: the 3.1 Computer Architecture journey · Add 3.1 Computer Architecture to a class →

3.2 Input and Output Devices (48 modules)

Keyboard An input device where pressing a key completes a circuit. The controller identifies the key and sends its character code to the computer, so text and commands can be entered.

Optical mouse An input device with an LED or laser under it that lights the surface while a sensor takes rapid images to track movement and move the pointer. It has no ball.

Microphone An input device that turns sound waves into an analogue electrical signal, which an ADC converts to digital data so the computer can record or process voice.

Digital camera Input device: a lens focuses light onto an image sensor of light-sensitive cells; each cell becomes a pixel of digital data, stored as an image file. More pixels give more detail.

Barcode scanner An input device that shines a laser across a barcode. Black lines absorb light, white gaps reflect it, and a sensor reads the pattern to get the product number.

QR code scanner Uses a camera to capture a 2D square grid of black and white modules and decodes it into data like a web address or text. It holds more data than a barcode and reads from any angle.

Barcodes compared with QR codes A barcode stores a short number in one dimension of lines; a QR code stores much more data in two dimensions of squares and can be read by a camera from any angle.

Touch screen A display that is also an input device: it detects where a finger or stylus touches it. Types are resistive, capacitive and infra-red. Used in phones, tablets, kiosks and ticket machines.

Resistive touch screen A screen with two conductive layers that touch when pressed; the change in resistance at the touch point gives its position. Works with finger, glove or stylus.

Capacitive touch screen A touch screen with a charged glass layer. A finger conducts electricity and changes the charge at the touch point, so its position is found. Supports multi-touch.

Infra-red touch screen A screen with a grid of infra-red beams across it. A touch breaks beams, and the broken x and y beams give the touch position. Works with any object.

Comparing resistive, capacitive and infra-red touch screens Resistive senses pressure on layers; capacitive senses a finger's electric charge; infra-red senses a broken light beam. How touch is detected decides which device each suits.

2D scanner An input device that moves a light and sensor across a flat page or photo, reading the reflected light to capture a digital image made of pixels.

3D scanner An input device that uses lasers, light patterns or cameras to measure many points on an object's surface and combine them into a digital 3D model of its shape.

Choosing a suitable input device for a context The input device that best captures the data needed and suits the user's situation. Justify it with 'because'. E.g. a microphone because it captures sound.

LCD screen Screen with a backlight shining through liquid crystals that twist to block or pass light. Red, green and blue filters on each pixel make its colour.

LED screen A screen that uses light emitting diodes as its light source, as a backlight for an LCD panel or as the pixels themselves. It is bright, thin and uses little power.

Comparing LCD and LED screens LCD screens use a fluorescent (CCFL) backlight; LED screens use LED backlights, so they are brighter, thinner, have better contrast and use less power.

LCD projector An output device: a bright lamp shines light through red, green and blue LCD panels that form the image, then a lens focuses the recombined light onto a screen.

DLP projector A projector with a chip of tiny mirrors (one per pixel) that tilt towards or away from the lens to make the image. A spinning colour wheel adds colour.

Comparing LCD and DLP projectors Both projectors show an image on a screen. LCD shines light through liquid crystal panels; DLP bounces light off tiny mirrors (micromirrors). They differ in sharpness, colour, size and cost.

Inkjet printer Sprays tiny droplets of liquid ink through nozzles in a print head onto paper as the head moves across it. Uses cyan, magenta, yellow and black cartridges.

Laser printer A printer that uses a laser to draw the image as static charge on a drum. Toner sticks to the charged areas, is transferred to paper, then fixed by a heated fuser.

Comparing inkjet and laser printers Inkjet sprays liquid ink: good photo quality, cheap to buy, costly per page. Laser fuses toner powder: fast, sharp text, dearer to buy, cheaper per page.

3D printer An output device that builds a solid object from a digital 3D design file by adding material, such as melted plastic, one thin layer at a time.

Speaker An output device that turns an electrical signal into sound. An electromagnet makes a cone vibrate, and the vibrations make sound waves. A DAC first converts digital sound to analogue.

Actuator An output device that turns a control signal from a processor into physical action, such as a motor turning, a valve opening or a heater switching on, in control systems and robots.

Choosing a suitable output device for a context Match the result needed (image, print, sound, 3D, movement) and the situation to the device that suits it best, then justify with 'because'.

What a sensor is An input device that measures a physical quantity, such as heat or light, from the environment and sends the readings to a computer or microprocessor.

Analogue sensor data and analogue-to-digital conversion Turns the continuously varying analogue readings from a sensor into digital values (binary numbers) so a computer can process them.

Acoustic sensor A sensor that detects sound and measures its level. Used in noise monitoring, burglar alarms and glass-break detection to show how loud a sound is or whether a sound is present.

Accelerometer sensor A sensor that measures acceleration (change in speed or direction) and tilt. Used for phone screen rotation, step counters and car airbag impact detection.

Flow sensor An input device that measures how much liquid or gas moves past a point in a set time (the flow rate). Used in water meters, fuel systems, pipelines and irrigation.

Gas sensor An input device that detects the presence or concentration of a particular gas in the air, e.g. in carbon monoxide alarms, gas leak detection, air quality checks and breathalysers.

Humidity sensor An input device that measures the amount of water vapour (moisture) in the air. Used in weather stations, greenhouses and air conditioning systems.

Infra-red sensor A sensor that detects infra-red radiation, such as heat given off by people and objects, or a broken infra-red beam. Used in burglar alarms and automatic doors.

Level sensor A sensor that measures how full a container is by detecting the height of a liquid or solid, e.g. in a water tank, fuel gauge or chemical vat.

Light sensor An input device that measures how bright the light is and sends the light level to a computer. Used in automatic street lights, screen brightness and greenhouses.

Magnetic field sensor An input device that detects the presence and strength of a magnetic field. Used in door alarms, compasses, wheel speed counters and metal detectors.

Moisture sensor An input device that measures the amount of water in a solid material such as soil. Used in automatic plant watering and farming. Not the same as a humidity sensor, which measures air.

pH sensor An input device that measures how acidic or alkaline a liquid is on the pH scale and sends the pH value to a computer. Used in water treatment, fish tanks, soil testing and food production.

Pressure sensor An input device that measures the force applied over an area by a gas, liquid or solid, e.g. in tyre pressure monitors, weather forecasting and pressure pads.

Proximity sensor A sensor that detects whether an object is nearby, or how far away it is, without touching it. Used in parking sensors, phones turning off the screen during calls and automatic doors.

Temperature sensor An input device that measures how hot or cold something is. Used in central heating, ovens, greenhouses and weather stations.

Sensors, microprocessor and actuator in a control system A sensor sends readings to a microprocessor, which compares them with a stored value and signals an actuator, such as a heater, to act. This repeats continuously.

Matching sensors to the data they capture Each sensor captures one type of data, so identify the data first (e.g. moisture in soil, humidity in air), then name the sensor that measures it.

Choosing the most suitable sensor for a given context The sensor that measures the physical quantity a system needs, e.g. light for street lamps or pressure for a car park. Justify it with 'because'.

Choosing input devices, output devices and sensors together for a system A complete system uses input devices or sensors to capture data and output devices or actuators to deliver results, each chosen to suit the task.

Just this content description: the 3.2 Input and Output Devices journey · Add 3.2 Input and Output Devices to a class →

3.3 Data Storage (28 modules)

Primary storage Memory the CPU can access directly, so it is fast. It is made up of RAM (temporary, holds running programs and data) and ROM (permanent, holds start-up instructions).

Volatile and non-volatile memory Memory that loses its contents when the power is off, like RAM. Non-volatile memory, like ROM and SSDs, keeps its data without power.

Read only memory (ROM) Read only memory: non-volatile primary storage whose contents are fixed. It keeps the start-up (boot) instructions, so data stays when power is off. Also used in embedded devices.

Differences between RAM and ROM RAM is volatile, read/write and holds running programs; ROM is non-volatile, read only and holds start-up instructions. RAM is larger.

Why a computer needs both RAM and ROM ROM holds the start-up instructions that survive power-off. RAM holds the changing operating system, programs and data in use. A computer needs both to start up and to run.

Secondary storage Non-volatile storage the CPU cannot access directly. It keeps data permanently, even when power is off. Data is copied to RAM before use. Types: magnetic, optical, solid-state.

Why secondary storage is needed Permanent, non-volatile storage with a much larger capacity than RAM. It keeps files, programs and the OS safe when the power is off, because RAM is volatile and too small.

Magnetic storage: platters, tracks and sectors A spinning circular disk in magnetic storage. Its surface is split into tracks (concentric circles) and sectors (sections of a track), where data is stored as magnetised areas.

Magnetic storage: reading and writing with electromagnets A read/write head uses an electromagnet to magnetise tiny areas of the spinning platter to store 1s and 0s, and reads the data back by detecting the magnetic pattern.

Hard disk drive (HDD) Hard disk drive: a magnetic storage device with spinning platters and moving read/write heads. It gives large capacity at low cost, but is slower and more fragile than flash.

Optical storage: pits and lands Dents (pits) and flat areas (lands) along a disc's spiral track. A laser reads them by how light reflects: lands reflect it back, pits scatter it. The changes store binary data.

Optical discs: CD, DVD and Blu-ray Optical discs read by laser. Capacity rises CD, DVD, Blu-ray as each laser's shorter wavelength packs pits closer. Blu-ray uses blue-violet. Discs are read-only or recordable.

Solid-state (flash) storage Storage that keeps data in flash memory chips with no moving parts. It is non-volatile, so data stays when power is off. Examples are SSD, SD card and USB drive.

Transistors as control gates and floating gates A flash memory cell: a transistor with a control gate and a floating gate that traps charge for one bit value and none for the other, so the bit stays stored when power is off.

NAND and NOR flash The two ways of arranging flash transistors, named after logic gates. NAND gives high capacity (SSDs, SD cards); NOR gives faster random reads (stored program code).

Examples of solid-state storage: SSD, SD card and USB drive Flash-based solid-state devices: an SSD is the main storage in a laptop, an SD card suits cameras and phones, and a USB drive is a portable stick for carrying files.

Comparing magnetic, optical and solid-state storage Three types of secondary storage that store data in different ways (magnets, laser pits, flash cells), so they differ in capacity, speed, durability, portability and cost.

Choosing a secondary storage device for a scenario Match a scenario's needs (capacity, speed, portability, durability, cost) to magnetic, optical or solid-state storage, then justify the choice with reasons.

Virtual memory Part of secondary storage (HDD or SSD) that the computer uses as extra RAM when real RAM is full. It is slower than RAM.

Why virtual memory is needed Part of secondary storage used as extra RAM, so a computer can run programs and data bigger than its RAM, with many programs open, without them failing when RAM is full.

How virtual memory is created Part of secondary storage that the operating system sets aside to hold pages of data when RAM is full. The OS manages this space and can make it bigger when more is needed.

Pages moving between RAM and virtual memory Data is split into fixed-size pages. Idle pages are moved out of RAM into virtual memory, then swapped back into RAM when the CPU needs them.

Virtual memory and computer performance When RAM is full, the computer keeps swapping pages to slow secondary storage, so it becomes sluggish. Adding more RAM reduces swapping. Virtual memory is no replacement for RAM.

Physical servers and storage behind the cloud A building full of servers and storage devices owned by the cloud provider. It holds users' data, often copied to several locations, and is accessed over the internet.

Advantages of cloud storage Saving data on a provider's remote servers so you can reach files from any device online, add space easily, get backups done for you and share files, without buying your own hardware.

Disadvantages of cloud storage Problems with saving data online: no internet means no access, ongoing subscription fees, data held by a third party that could be hacked, and slow transfers of large files.

Comparing cloud storage with local storage Cloud storage is accessed over the internet from anywhere, but relies on a network and provider. Local storage is on your device: quicker and fully under your control, but less portable.

Writing exam answers about data storage A full-mark storage answer uses the correct term (e.g. virtual memory, ROM, SSD) and links each point to a reason with 'because', rather than just naming or listing things.

Just this content description: the 3.3 Data Storage journey · Add 3.3 Data Storage to a class →

3.4 Network Hardware (19 modules)

What a MAC address is A unique hardware address given to one network interface card (NIC). Each NIC has its own, so a device with Wi-Fi and Ethernet has two. It identifies the hardware, not the network.

MAC addresses are given at manufacture A MAC address is set by the manufacturer when the NIC is made and stored in the NIC, so it normally stays the same on any network the device uses.

MAC address format A MAC address is six pairs of hex digits (two digits per pair, 48 bits in total), separated by colons or hyphens, such as 00:1A:2B:3C:4D:5E.

Manufacturer code and serial code in a MAC address First 3 pairs (00:1A:2B) are the manufacturer code; last 3 pairs (3C:4D:5E) are the serial code that makes this NIC unique.

Purpose of a MAC address A unique address that identifies a device's NIC, so data on a local network is delivered to the correct device.

IP addresses are allocated by the network A device is given its IP address by the network it joins, not by the manufacturer, so it can change on a new network. Unlike a MAC address, it is not built into the NIC.

IPv4 address format 32 bits written as four denary numbers from 0 to 255 separated by full stops, such as 190.0.5.20. Each number is a group of 8 bits.

Spotting an invalid IPv4 address An address without exactly four groups, or with a group outside 0 to 255. Examples: 256.1.1.1 (too big), 192.168.1 (too few groups), 10.-5.2.1 (negative) and 10.a.2.1 (letter).

The limited number of IPv4 addresses The number of possible IPv4 addresses (about 4.3 billion). It is too few for every phone and smart device online, so a new version, IPv6, was needed.

IPv6 address format A 128-bit address written as eight groups of four hex digits separated by colons, e.g. 2001:0DB8:0000:0000:0000:FF00:0042:8329

Shortening an IPv6 address Replaces one run of all-zero groups in an IPv6 address, and can be used only once. Leading zeros in each group can also be dropped, e.g. 0db8 becomes db8.

Comparing IPv4 and IPv6 A 128-bit address written in hex with colons. It gives vastly more addresses than 32-bit denary IPv4, which solves the shortage of IPv4 addresses.

Static IP address An IP address that is set once, usually by hand, and stays the same every time the device connects, so the device always has a predictable address.

Dynamic IP address An IP address given to a device automatically by the network each time it connects, so it may change and can later be reused by another device.

Choosing static or dynamic IP for a device Use static for devices others must always find, like web servers and printers; use dynamic for phones and laptops because it needs less set-up work.

Differences between a MAC address and an IP address MAC is fixed by the manufacturer and stays the same, written in hex. IP is given by the network and can change, written in denary (IPv4) or hex (IPv6).

Why a device needs both a MAC address and an IP address The IP address shows where a device is on the network so routers can route data to it. The MAC address identifies its physical NIC for local delivery. Both are used to deliver data.

A router assigns IP addresses A router on a local network gives each device that joins its own IP address automatically, so nobody sets it up by hand. Every device gets a different address.

Writing exam answers about network hardware and addresses A full-mark answer uses the correct terms (NIC, MAC address, IP address, router) and links each point to a reason, using 'because'.

Just this content description: the 3.4 Network Hardware journey · Add 3.4 Network Hardware to a class →

4.1 Types of Software and Interrupts (39 modules)

System software Software that provides the services the computer needs to run, such as the operating system and utility software, often working in the background without the user asking.

Examples of application software Software named by the user task it does, such as a word processor, spreadsheet, web browser, photo or video editor, or game, so the user can get a job done.

System software versus application software System software runs the computer itself, e.g. the OS. Application software does jobs for the user, e.g. a word processor, and cannot run without system software.

Utility software System software that helps maintain, look after and protect a computer, such as antivirus, backup and file compression. It is separate from the operating system.

Disk defragmentation utility A utility that rearranges the scattered pieces of files on a hard disk drive so each file is stored together, which speeds up reading. It is not needed for SSDs.

Disk formatting utility Utility software that prepares a new drive or USB stick for use by creating a file system to store files in. It also erases any existing data on the device.

File compression utility Utility software that makes files smaller to save storage space and send them faster, and can restore (unzip) them to their original form when needed.

Classifying software as system or application Ask who the program serves: the computer itself (OS, antivirus, backup) is system software; a task the user wants done (word processor, game) is application software. Justify with 'because'.

The nine functions of an operating system The nine jobs of an OS: managing files, handling interrupts, user interface, peripherals and drivers, memory, multitasking, platform for apps, security and user accounts.

OS function: managing files An OS function that keeps track of files and folders, lets users create, name, open, copy, move and delete them, and records where each file is stored.

OS function: providing a graphical user interface (GUI) Graphical user interface: the user controls the computer with windows, icons, menus and a pointer instead of typing commands. It suits beginners but uses more system resources than a CLI.

OS function: providing a command-line interface (CLI) A user interface where you type text commands to control the computer. It is precise and quick for experts, uses few resources, but is harder to learn because commands must be remembered.

OS function: managing peripherals and drivers The OS controls data passing to and from peripherals and loads the correct driver for each device so it can be used. Without a driver, the device does not work.

OS function: managing memory The OS decides which part of RAM each running program uses, keeps programs from overwriting each other's memory, and frees the space when a program closes.

OS function: managing multitasking The OS runs several programs at once by sharing CPU time in very short slices and switching quickly between them, so they appear to run together.

OS function: providing a platform for running applications The OS provides a platform: a standard environment and shared services that apps ask for, so a program uses hardware through the OS instead of controlling it directly.

OS function: providing system security An OS function that protects the computer and its data from unauthorised access and attack using logins, access rights, updates and security tools.

OS function: managing user accounts An OS function that creates, stores and controls user accounts, so each user logs in with a username and password and gets their own settings, files and access rights.

Matching a scenario to an operating system function Find what the OS is doing in a scenario, such as sharing the CPU, loading a driver or checking a password, then match it to one of its nine functions and explain with 'because'.

Firmware Permanent software stored in a chip on the hardware. It gives the hardware its basic instructions and is kept when the power is off. Found in routers and PCs.

Bootloader A small program stored in firmware that runs first at power-on, finds the operating system on storage, copies it into RAM and hands control to it.

The start-up sequence of a computer Power on, the bootloader in firmware runs and loads the OS from storage into RAM (which is empty at power-on). Once the OS is ready, the user can open applications.

Layers: applications, operating system, firmware and hardware The layers of a computer: applications run on the operating system, which runs on firmware, which runs on hardware. Each layer depends on the layer below it.

Why an application needs the operating system, firmware and hardware An application cannot run on its own: it needs the OS to manage resources, the firmware to start the OS and the hardware to carry out its instructions.

Interrupt A signal sent to the CPU telling it to pause its current task so something more urgent can be dealt with. The CPU then returns to the original task. It is not a crash.

Why computers use interrupts A signal that tells the CPU an event needs attention, so it responds only when needed instead of constantly checking devices (polling). This frees the CPU and gives a quick response.

Hardware interrupts A signal sent by a hardware device, such as a keyboard, mouse or printer, to tell the CPU it needs attention, for example a key press or a printer out of paper.

Software interrupts A signal sent to the CPU by a program or the processor itself when a process hits an error (e.g. divide by zero, invalid instruction) or needs an OS service, so the CPU pauses it.

Hardware interrupts compared with software interrupts A hardware interrupt comes from a device outside the program (key press, mouse move); a software interrupt comes from the running program itself (divide by zero, memory conflict).

Classifying an event as a hardware or software interrupt The origin of the signal. From a device, like a key press or mouse move, it is a hardware interrupt. From a running program, like divide by zero or a memory clash, it is a software interrupt.

How an interrupt is generated A signal sent to the CPU by a device (hardware) or a running program (software) when an event, such as a key press, needs the CPU's attention.

The CPU checks for interrupts after each cycle At the end of each fetch-decode-execute cycle the CPU checks for an interrupt signal. If none, it fetches the next instruction; if one, it switches to handling it first.

Interrupt priority Each interrupt has a priority level. The CPU handles the most urgent one first, so a power failure can pause the handling of a less urgent key press.

Interrupt service routine (ISR) A small program the CPU runs to deal with one particular interrupt. Each type of interrupt has its own ISR, kept in memory, and it is short so the CPU can quickly return to its task.

Saving the CPU's state before handling an interrupt Before running the ISR, the CPU stores its register contents, including the program counter, so the interrupted task can later carry on exactly where it stopped.

What happens as a result of an interrupt What the ISR does depends on the event: it reads a key press, updates the pointer, shows an error or stops a faulty program. Then the CPU resumes the task it was running.

Interrupt handling step by step The ordered steps: an interrupt is generated, the CPU finishes its cycle and detects it, saves its state, runs the ISR, restores its state, then resumes the original task.

OS function: handling interrupts The OS receives each interrupt, picks the right ISR to run, manages priorities, then passes control back to the interrupted program so it can carry on.

Writing an exam answer about software and interrupts A full-mark answer uses the correct terms (system software, firmware, bootloader, ISR), gives points in the right order, and adds a reason for each point.

Just this content description: the 4.1 Types of Software and Interrupts journey · Add 4.1 Types of Software and Interrupts to a class →

4.2 Programming Languages, Translators and IDEs (35 modules)

Program and source code The instructions a programmer writes in a programming language. The CPU cannot run it until a translator turns it into machine code.

High-level language A programming language using English-like words that is easy for people to read and write, such as Python or Java. One statement does many jobs, and it must be translated before the CPU can run it.

Low-level language A programming language close to the CPU's instructions, such as machine code or assembly language. Each instruction is one simple CPU operation, so it is harder for people to read.

Ease of reading and writing code: high-level vs low-level Code that uses familiar words, so it is easier to read and write than low-level code, which needs many detailed instructions to do the same job.

Ease of debugging: high-level vs low-level Debugging is finding and fixing errors. It is easier in short, readable high-level code than in long, hard-to-read low-level code, and translators give clearer error messages for it.

Machine independence A language whose code can run on different types of computer. High-level languages are machine independent (portable); low-level languages are machine dependent.

Direct manipulation of hardware Low-level code can work directly with hardware, such as registers and memory locations, which high-level languages usually hide from the programmer.

Advantages and disadvantages of high-level and low-level languages High-level is easy to read, debug and portable but gives less hardware control; low-level is hard to read and machine dependent but gives direct hardware control.

Choosing a language level for a scenario Pick high-level for portable programs on many machines; pick low-level for direct hardware control, like drivers. Then justify the choice by linking it to the task's needs.

Mnemonics in assembly language A short, memorable code in assembly language, such as LDA, ADD or STO, that stands for one machine code instruction and is easier to remember than binary.

Assembler A translator that converts an assembly language program into machine code, so the CPU can run it. Each mnemonic becomes one machine code instruction.

Why translators are needed Software that converts high-level or assembly code into machine code, because the CPU can only run machine code. Types: assembler, compiler, interpreter.

Syntax errors and run-time errors reported by translators Code that breaks the rules of the language, like a missing bracket. The translator reports it and its line. A run-time error only occurs when the program runs.

Compiler A translator that converts a whole high-level language program into machine code in one go, before the program is run. The machine code can then run without the source code.

Executable file The machine code program a compiler produces. It runs without the compiler or source code, needs no re-translation, and works only on the type of machine it was made for.

Compiler error reporting A list of every error found after the compiler checks the whole program, with line numbers and error types. No executable is made and nothing runs until all are fixed.

Interpreter A translator that translates a high-level program one line at a time and runs each line straight away. It makes no executable file, so the source code and interpreter are needed on every run.

Interpreter error reporting An interpreter runs code line by line and halts at the first error it finds, reporting only that one. Earlier lines have already run. Later errors stay hidden until you fix it and run again.

Advantages of a compiler A program translated all at once into an executable. It runs faster, needs no compiler to run, keeps the source code private, and gives a whole-program error report.

Disadvantages of a compiler A compiler must translate the whole program without errors before any of it runs, and its executable only works on one machine type, so testing small changes is slow.

Advantages of an interpreter Runs code line by line with no wait to compile, so unfinished programs can be tested at once. It stops at the faulty line, making errors easy to find. Source code runs on any machine with one.

Disadvantages of an interpreter An interpreter translates the source code again on every run, so programs run slower and need the interpreter and source code each time. Only one error is shown at a time.

Comparing a compiler and an interpreter A compiler translates the whole program into an executable before it runs; an interpreter translates and runs line by line, stopping at the first error, with no executable.

Interpreter for development, compiler for the final program Use an interpreter while developing to test and fix code quickly, then compile the final program once into a fast executable to give users without the source code.

Choosing a translator for a scenario Pick an assembler for assembly code, an interpreter while testing a program, or a compiler for release to customers, then justify your choice using 'because'.

Integrated development environment (IDE) Integrated development environment: one program, such as IDLE, Thonny or Visual Studio, with the tools to write, run and test code. It is not a language or a translator.

IDE function: code editor The part of an IDE where you type and edit source code. It shows line numbers and syntax highlighting (colour-coded keywords), which a plain text editor does not.

IDE function: run-time environment An IDE feature that lets you run your program and see it work, including its input and output, without leaving the IDE. It has a run button, a console and can step through code.

IDE function: translators A compiler or interpreter built into an IDE, so the programmer can translate and run code from one button without needing separate translator software.

IDE function: error diagnostics An IDE tool that finds errors in code and tells the programmer where they are and what kind they are, using line numbers, error messages, highlighting and debugging tools.

IDE function: auto-completion An IDE feature that suggests or finishes a keyword, function or variable name as you start typing it. It saves time and cuts spelling mistakes in names.

IDE function: auto-correction An IDE feature that fixes, or suggests fixes for, simple mistakes like a misspelt keyword or a missing bracket. The programmer can accept the fix, so fewer syntax errors occur.

IDE function: prettyprint An IDE feature that shows code in a clear layout, using colours for keywords and indentation for blocks, so it is easy to read. It changes only the display, not the code.

Matching an IDE function to a need A built-in IDE tool that solves one programmer problem, so you match a need (typing, running, finding errors, saving typing, fixing, tidying) to the right function.

Writing exam answers about languages, translators and IDEs A full-mark answer states a point with the correct term, then links it to a reason, e.g. a compiler runs faster because the whole program is already translated.

Just this content description: the 4.2 Programming Languages, Translators and IDEs journey · Add 4.2 Programming Languages, Translators and IDEs to a class →

5.1 The Internet and the World Wide Web (33 modules)

Website and web page A collection of linked web pages stored on web servers. A web page is a single document viewed in a browser, and the web is made up of many websites.

Hypertext and hyperlinks Text that contains hyperlinks. Clicking a link takes you to another web page or file. Links join pages together, which is why the web is called a web.

What a URL is Uniform Resource Locator: a text-based address that identifies a unique web page or file, typed into the browser address bar. It is the address, not the page content.

URL part: the protocol The protocol at the start of a URL. It tells the browser which set of rules to use to fetch the page: http:// is unencrypted, https:// is secure. The :// separates it from the rest.

URL part: the domain name The human-readable name of a website's host in a URL, made of the www prefix and a top-level domain like .com or .org. It is easier to remember than a number.

URL part: the web page or file name The last part of a URL. It names the web page or file wanted: folders (the path) then the file name, like shoes.html. With no file name, the server sends a default page.

Splitting a URL into its parts A URL splits into protocol (https), domain name (www.example.com) and web page or file name (shop/index.html). Each part can be labelled.

Purpose of HTTP Hypertext Transfer Protocol: the set of rules a browser and web server use to request and send web pages. It is the default protocol for the web and is used only for web pages.

HTTP request and response The browser sends an HTTP request asking for a page. The web server sends back an HTTP response with the page's HTML, or an error such as 404 page not found.

HTTP compared with HTTPS HTTP plus SSL/TLS encryption. Plain HTTP sends readable text that can be intercepted; HTTPS scrambles data so intercepted data can't be read, and a certificate shows the site is genuine.

What a web browser is Software that requests web pages from web servers and displays them to the user, e.g. Chrome, Firefox, Safari or Edge. It is the client, and it is not a search engine.

Browser function: address bar The part of a browser where the user types a URL to visit a page. It also shows the URL of the current page and a padlock when the site is secure.

Browser function: bookmarks and favourites A saved URL (also called a favourite) in a web browser that lets the user return quickly to a web page without typing its address again.

Browser function: recording history A list of the URLs of web pages a user has visited, usually with dates, so they can find a page again. The user can clear it.

Browser function: multiple tabs A browser feature that keeps several web pages open at once in one window, so you can open a new tab and switch between pages without losing your place.

Browser function: navigation tools Browser buttons such as back, forward, refresh and home that let the user move between web pages, reload the current page and return to a starting page.

Browser function: storing cookies A small file a website sends to your browser. The browser stores it on your device and sends it back to that website on later visits. Browser settings can block or delete it.

Matching a browser function to a need A browser tool that meets a user need: bookmarks return to a favourite site, tabs open many pages at once, history finds an old page, back goes one page.

Why domain names are used instead of IP addresses An easy-to-remember name, like example.com, that stands in for a numeric IP address. It must be converted into the IP address before the computer can find the web server.

Domain name server (DNS) Domain name server: stores a list of domain names with their matching IP addresses. Give it a domain name and it returns the IP address. Many DNS servers exist across the internet.

A DNS lookup step by step The browser sends a domain name to a DNS server, which searches for it and returns the matching IP address. If it has no match, it passes the request to another DNS server.

Web server A computer that stores website files and sends them to a browser (the client) over the internet using HTTP when the browser asks for a page. It is always switched on and connected.

Requesting a page from the web server A message the browser sends to the web server's IP address asking for a page; the server replies with the page's HTML, or an error such as 404 if it does not exist.

From URL to web page: the full sequence The ordered steps after you enter a URL: the browser asks DNS for the IP address, sends a request to the web server, gets HTML back, then renders the page.

Session cookies A cookie stored temporarily in memory while you browse. It has no expiry date, lasts only for one visit and is deleted when the browser is closed.

Persistent cookies A cookie saved on the device until its expiry date or until the user deletes it, so it stays after the browser closes and is sent again on later visits.

Comparing session and persistent cookies A session cookie is deleted when the browser closes; a persistent cookie is kept on the device until it expires. Cookies are text data, not programs.

Cookie use: saving personal details A cookie can save personal details like your name or address, so forms are autofilled and you are greeted by name on later visits. A persistent cookie suits this.

Cookie use: tracking user preferences A cookie that records a user's preferences and browsing habits so a site can tailor what it shows, such as language, layout, suggested products or targeted adverts.

Cookie use: holding items in an online shopping cart A cookie that remembers which items a user has added to an online shopping cart, so the cart is not emptied as they move between pages. It can last one visit or be kept for later.

Cookie use: storing login details A small file a website saves in your browser to remember you are logged in, so you do not have to type your username and password on every page.

Choosing session or persistent cookies for a scenario Decide how long a cookie must last: session if it can go when the browser closes, persistent if it must last for later visits. Justify your choice with because.

Writing exam answers about the internet and the web An exam answer that uses correct terms (URL, DNS, HTTP), gives each step in order and explains why, e.g. DNS finds the IP address so the browser knows which server to ask.

Just this content description: the 5.1 The Internet and the World Wide Web journey · Add 5.1 The Internet and the World Wide Web to a class →

5.2 Digital Currency (25 modules)

What a currency is The money a country or group uses to buy, sell and store value, such as the dollar or the pound.

Physical money: coins and notes Cash in the form of coins and notes that you can hold in your hand and hand over to pay for things, unlike digital currency, which exists only electronically.

Digital currency Money that only exists electronically as data on computers. It has no coins or notes, cannot be held in your hand, and is stored and sent using devices.

Digital currency compared with physical cash Both pay for goods, but digital currency exists only as electronic records in a wallet, sent over a network with a device and connection, while cash is physical coins and notes handed over.

Cryptocurrency as an example of digital currency A kind of digital currency, such as Bitcoin or Ethereum, that exists only electronically and is not printed or controlled by a government or central bank.

Digital wallets Software or an app on a phone or computer that stores a person's digital currency and is used to send and receive it. Losing access to it can mean losing the currency.

Using digital currency to pay for goods and services Spending digital currency online or in shops that accept it to buy goods and services. The payment is sent from your wallet app as an electronic transaction.

Using digital currency to send money to other people Sending digital currency straight from one person's wallet to another's over the internet, even in another country, using the receiver's wallet address. No coins or notes are posted.

Using digital currency as an investment Buying digital currency and holding it, hoping its value rises so you can sell it for a profit. Its value can also fall, so you could lose money.

Advantages and risks of digital currency Digital currency is fast and easy to send, but its value can change quickly, hackers can steal it, a lost password loses access, and not every shop accepts it.

Transaction A single movement of money from one person to another, such as a payment of an amount from a sender to a receiver. Each one must be recorded.

Ledger A record book listing every transaction, so you can see who paid whom and how much. It is used to work out balances and keep an accurate history.

Digital ledger A ledger stored electronically instead of on paper. Records are kept as data on computers, so they are easy to search and copy. Digital currency uses one to track who owns what.

What a ledger record contains One entry in a ledger that states who sent the money (sender), who received it (receiver) and how much was sent (amount). Each transaction gets its own record.

Time-stamp The date and time added to a record when it is created, showing when it was made. It puts records in order and shows which happened first.

A record that cannot be altered Cannot be changed or deleted once added. A blockchain record stays fixed, so mistakes are fixed by adding a new record and the history stays permanent.

Why records that cannot be altered matter A record that cannot be changed once saved, so no one can cheat by editing an amount or deleting a payment, and everyone can trust the ledger.

Blockchain A digital ledger: a time-stamped series of records, in order, that cannot be altered.

Blocks of transactions A group of transaction records saved together with a time-stamp as one unit of the blockchain. When a block is full it is closed, and new transactions go into a new block.

Blocks joined in a chain Blocks are added one after another in time order. Each new block goes on the end and links to the block before it, so the blocks form a chain.

Copies of the blockchain shared across many computers A blockchain ledger copied on many computers. No one person or company controls it, and a changed copy is spotted by comparing it with the others.

Following one digital currency transaction through the blockchain The order a payment follows: the sender makes it, it is time-stamped, placed in a block, and the block joins the chain, so the record becomes permanent.

Working out ownership from the blockchain The amount of digital currency a person owns, found by adding up all the money they received and taking away all the money they sent in the blockchain records, in time order.

Stopping the same digital currency being spent twice Spending the same digital currency twice. Blockchain stops it: each spent payment is already in the shared ledger, so a second payment of the same money is refused.

Writing exam answers about digital currency and blockchain A full-mark answer uses digital currency, ledger, time-stamp and blockchain correctly, and links each point to a reason, using linking words such as because or so that.

Just this content description: the 5.2 Digital Currency journey · Add 5.2 Digital Currency to a class →

5.3 Cyber Security (15 modules)

Trojan horse Malware disguised as useful or harmless software. The user installs it willingly, then it secretly does harm, such as opening a back door or stealing data. It does not replicate itself.

Adware Software that shows unwanted adverts, such as pop-ups, often installed with free programs, to earn money for its creator. It can slow a device, redirect searches and track users.

Distributed denial of service (DDoS) attack A botnet of infected computers floods one server with requests at the same time, so it cannot respond to real users and the website goes offline.

The domain name server (DNS) and IP addresses A domain name server translates a domain name typed in a browser, such as example.com, into the IP address of the web server that holds the website.

Pharming An attack that redirects a user to a fake website, even when they type the right address, using malicious code or DNS poisoning, so the site can steal their login and payment details.

Phishing Sending many fake emails that look genuine to trick users into clicking a link or replying with personal details, so criminals can steal passwords and bank details.

Matching a threat to its process and aim Match a threat by finding its process (how it works) and its aim (why the attacker does it), e.g. phishing: fake emails trick users to steal login details.

Access levels Settings that give each user different rights to data: no access, read only, read/write or full control. Users only see and change what their role needs, protecting confidentiality and integrity.

Anti-spyware software Software that scans for and removes spyware, and blocks programs that secretly monitor the user, such as key loggers. It can scan on demand or protect in real time.

What a proxy server is A server between a user's device and the internet. It receives the user's web requests, passes them to the web server for the user, then returns the response. Used in schools and companies.

How a proxy server keeps data safe A server between a user and the internet that filters requests, blocks unsafe sites, hides the user's IP address, checks responses for malware and caches pages for speed.

Secure socket layer (SSL) protocol Secure Socket Layer: a security protocol that encrypts data between a browser and web server, so intercepted data cannot be read. Used for logins and payments. TLS is its successor.

SSL certificates and the handshake Browser asks the server for its digital certificate, checks it is genuine, then both agree an encryption key to begin a secure session.

Choosing a solution to counter a threat A solution chosen to stop a specific threat, such as a firewall for hacking, SSL for interception or anti-malware for malware, plus an explanation of how it works.

Writing exam answers about cyber security A full-mark answer names the threat, says how it works and what it aims to do, then names a solution and explains how it stops the threat, using 'because' to link each point.

Just this content description: the 5.3 Cyber Security journey · Add 5.3 Cyber Security to a class →

6.1 Automated Systems (28 modules)

What an automated system is A system that senses its surroundings, decides what to do and acts, without a person controlling each step. For example, an automatic door.

Comparing a sensor reading with a stored value A pre-set value, such as a target temperature, kept in the microprocessor. It compares each digital sensor reading with it to decide if the reading is too high, too low or on target.

Feedback in an automated system When an actuator's effect changes the next sensor reading, so the system keeps adjusting itself until the stored value is reached, e.g. a heater warms the room until the target.

Describing how an automated system works Describe the system: the sensor measures, the microprocessor compares the reading with a stored value, the actuator responds, and the process repeats.

Automated systems in industry Sensors send readings to a microprocessor, which controls actuators like motors, valves and robotic arms to run a production line or chemical plant with little human control.

Automated systems in transport A vehicle or traffic system where sensors send data to a microprocessor, which controls actuators to steer, brake or signal without a driver controlling every action.

Automated systems in agriculture Sensors, a microprocessor and actuators keep crop conditions right, such as watering or heating a greenhouse, without a farmer checking all the time.

Automated systems in weather monitoring A system where sensors and a microprocessor record weather readings at set intervals and send the data on without a person present, often in remote places, to help forecasting.

Automated systems in gaming Sensors in a controller or headset send readings to a microprocessor, which changes what the player sees or feels, such as moving the view or making the controller vibrate.

Automated systems in lighting Lights switched on, off or dimmed by sensors and a microprocessor with no one touching a switch, e.g. a street lamp that comes on when its light sensor detects dusk.

Automated systems in science Sensors and a microprocessor measure and control conditions in experiments, and collect data in places too dangerous or remote for people, such as volcanoes or space.

Advantage: works continuously An automated system runs 24 hours a day with no tiredness or breaks, so it can monitor and control a process all the time and react quickly to every sensor reading.

Advantage: accuracy and consistency An automated system repeats a task in exactly the same way every time, with no tiredness or human error, so its results are more accurate and consistent than human work.

Advantage: safety in dangerous places An automated system can work in hazardous or hard-to-reach places, such as toxic chemicals, volcanoes, deep sea or space, so people are not put at risk.

Advantage: lower running costs and fewer errors An automated system can cut costs over time as it needs fewer paid workers and wastes less material, energy or time, though buying it costs a lot at the start.

Disadvantage: cost to buy, install and maintain Automated systems are expensive to buy, install and maintain because they need sensors, microprocessors, actuators and skilled technicians.

Disadvantage: job losses and lost skills Automated systems can replace workers, causing unemployment, and fewer people keep practical skills. Retraining is needed. Example: a driverless train replacing drivers.

Disadvantage: faults, power cuts and hacking When an automated system stops working or is harmed, for example by a faulty sensor, a power cut or hacking, so the whole process may fail. A backup or manual control helps.

Disadvantage: cannot judge unexpected situations An automated system only follows its program and sensors, so it has no human judgement when something unexpected happens (like an odd obstacle). People are still needed to oversee it.

Human oversight of an automated system People set up, monitor and maintain an automated system, fix faults and can override it in an emergency, so automated does not mean no people are needed.

Advantages and disadvantages of automation in industry Weigh what a factory gains (nonstop work, steady quality, safety) against its costs (set-up cost, job losses, breakdowns), link points to the scenario, then conclude.

Advantages and disadvantages of automation in transport Compare what automated vehicles and signals gain (fewer driver errors, steady speed, no tiredness) with risks (sensor failure, hacking, job losses), linking each point to the scenario.

Advantages and disadvantages of automation in agriculture Sensors and actuators water crops and control climate. Pros: constant monitoring, less water wasted, less labour. Cons: high cost, sensor faults can kill crops, power cuts.

Advantages and disadvantages of automation in weather monitoring Weigh benefits like remote sites, readings day and night and no staff at risk against cost, storm damage, power supply and remote repairs, linking each point to the scenario.

Advantages and disadvantages of automation in gaming Weigh the benefits of sensor-based game controls (natural, immersive, accessible) against drawbacks (hardware cost, misread movement, space needed), linking each to the scenario.

Advantages and disadvantages of automation in lighting Weigh benefits (saves energy, safer at night, no switching) against drawbacks (install cost, sensor faults, animal false triggers) and link each point to the scenario.

Advantages and disadvantages of automation in science Weigh the benefits of automatic data collection (accurate readings, safe in danger) against the drawbacks (cost, faults, no judgement), linking each point to the science scenario.

Writing exam answers about automated systems Use these terms in order in an exam answer: the sensor reads, the microprocessor compares and decides, the actuator acts. Tie each point to the scenario and explain it with 'because'.

Just this content description: the 6.1 Automated Systems journey · Add 6.1 Automated Systems to a class →

6.2 Robotics (25 modules)

What robotics is The branch of computer science that covers the design, construction and operation of robots.

What a robot is A machine that carries out tasks automatically by following a program, usually without a person controlling each action. It does not have to look human.

Characteristic of a robot: mechanical structure or framework The physical body or framework of a robot, such as its frame, joints, arms or wheels, that holds its parts together and lets it move. A program alone is not a robot.

Characteristic of a robot: electrical components Parts such as sensors, a microprocessor and actuators, powered through wiring, that let a robot sense its surroundings, decide what to do and then move.

Characteristic of a robot: programmable A robot is programmable: it follows a stored set of instructions, and changing the program changes what the robot does. With no program it cannot act.

The three characteristics of a robot together A device is a robot only if it has all three: a mechanical structure, electrical components and a program. If any one is missing, it is not a robot.

Deciding whether a device is a robot Check a device for all three robot characteristics: mechanical structure, electrical components and a program. Then justify with 'because' and evidence from the description.

Example robot: factory equipment A factory robot with a jointed frame and gripper, electric motors and sensors, and a program that repeats a task on each item on a production line.

Example robot: domestic robots A robot used in the home, such as a robot vacuum cleaner or lawnmower, that senses its surroundings and moves automatically to do a household job.

Example robot: drones A flying robot with a frame and rotors, sensors, a microprocessor and motors, and a program that controls its flight, either by remote control or by following a programmed route.

Role of robots in industry A robot used in factories to do repetitive or dangerous jobs such as welding, spray painting, assembling and packing, often on car assembly lines or in hot, hazardous places.

Role of robots in transport Robots move people and goods, for example driverless cars, delivery drones and warehouse robots, using sensors to detect obstacles.

Role of robots in agriculture A robot that does farm jobs such as planting, picking, spraying and monitoring crops, e.g. fruit-picking robots, spraying drones, milking machines and soil sensors.

Role of robots in medicine Robots help with medical tasks needing great accuracy or care, such as assisting in surgery, moving patients and delivering supplies in hospitals.

Role of robots in domestic settings A robot that does household jobs, such as vacuuming floors, mowing lawns or cleaning windows, saving people time and effort at home.

Role of robots in entertainment A robot used in toys, games, theme parks and film that moves or interacts to amuse people, such as robot pets, animatronics, drone light shows and film effects.

Matching a robot task to its role The area a robot works in: industry, transport, agriculture, medicine, domestic or entertainment. Match the task to the area, e.g. picking strawberries is agriculture.

Advantage of robots: safer work Robots can do dangerous tasks, such as working with heat, chemicals or heavy loads, so people are not put at risk of injury.

Advantage of robots: consistent and continuous work A robot repeats a task with the same accuracy every time and works for long periods without tiredness or breaks, so it raises productivity.

Advantage of robots: lower long-term running costs Robots cost a lot to buy, but over time they save money because they need no wages or holidays and make fewer mistakes, so less is wasted. The purchase cost is paid back.

Disadvantage of robots: job losses When robots do tasks that people did, fewer workers are needed, so some people lose their jobs. Workers may need retraining, though new jobs appear in building and maintaining robots.

Disadvantage of robots: high cost Robots are expensive to buy, install, program and maintain, so they can be too costly for small businesses.

Disadvantage of robots: limits and breakdowns A robot can only do what it is programmed to do, cannot use human judgement, and stops working if it breaks down or loses power. It is less flexible than a person.

Weighing the advantages and disadvantages of using a robot Compare a robot's advantages and disadvantages for one task, link each point to a reason with because, then give a conclusion on whether the robot should be used.

Writing exam answers about robotics Use the key terms robot, sensor, microprocessor, actuator and program correctly, and link each point to a reason, e.g. a robot is programmable so it can repeat a task.

Just this content description: the 6.2 Robotics journey · Add 6.2 Robotics to a class →

6.3 Artificial Intelligence (26 modules)

Artificial intelligence (AI) A branch of computer science dealing with the simulation of intelligent behaviour by computers. The computer imitates intelligence; it is not alive.

Intelligent behaviour in a computer A computer does a task that normally needs human thinking, like diagnosing a fault or choosing a game move, but it only simulates thinking and does not truly understand.

The two types of AI in this course The 0478 course covers only two types of AI. An expert system uses stored facts and rules to give advice. Machine learning learns from data to improve. Other kinds of AI are not examined.

AI characteristic: a collection of data and rules An AI system stores data (facts) and rules that say how to use them, such as a medical system matching symptoms to illnesses. Data without rules is not AI.

AI characteristic: the ability to reason An AI system reasons when it applies its rules to its data to work out a new conclusion that was not stored directly, instead of just looking up a saved answer.

AI characteristic: the ability to learn and adapt An AI characteristic where a system changes its own behaviour as it gains new data or experience, so it improves over time. Some AI systems can do this, but it is not required.

The main characteristics of AI together The three main characteristics of AI are a collection of data and rules, the ability to reason, and possibly the ability to learn and adapt. Learning and adapting is optional.

Identifying AI characteristics in a scenario Read a scenario and find the data and rules, the reasoning, and any learning. Then quote evidence from the description, using the word because to link each quote to the characteristic it shows.

Expert system An AI system that uses the knowledge and rules of human experts to give advice or answers on one specialist subject. It asks the user questions and gives a conclusion.

Examples of expert systems The expert knowledge that expert systems supply in areas like medical diagnosis, fault finding, mineral prospecting and financial advice, so the user does not need to be an expert.

The four parts of an expert system The four parts of an expert system: the knowledge base holds facts, the rule base holds rules, the inference engine reasons, and the interface talks to the user.

Knowledge base The part of an expert system that stores facts and information about a subject, gathered from human experts. It can be updated with new facts. The rule base holds the rules.

Rule base The part of an expert system holding IF-THEN rules (IF condition THEN conclusion) that link facts to conclusions, often joined with AND/OR, which the inference engine uses to reach answers.

Inference engine The part of an expert system that reasons: it matches the user's answers and the knowledge base against the rule base to reach a conclusion. It is the 'brain' of the system.

Expert system interface The part of an expert system the user sees. It shows questions, lets the user enter answers and facts, and displays the conclusion in a simple way for non-experts.

How an expert system reaches a conclusion The user answers questions at the interface; the inference engine applies the rules to the answers and knowledge base; the interface then shows the result.

Tracing an expert system to a conclusion Follow the user's answers through the IF-THEN rules in order, checking which rules fire and which do not, until one rule gives the final conclusion.

Machine learning A type of AI where a program automatically adapts its own processes and/or data, improving with experience, with no programmer changing it.

Machine learning adapting its own processes A machine learning program changes its own processes, meaning how it makes decisions, using what happened before, so no human has to rewrite the code.

Machine learning adapting its own data A machine learning program changes its own stored data by adding, updating or removing items as it meets new cases, e.g. spam marked by users, and uses that data in later decisions.

Machine learning compared with a fixed program A program that changes its own processes or data using feedback, so its results improve over time. A fixed program never changes: it follows the same instructions every time.

Examples of machine learning A program that improves from experience, e.g. spam filters, shopping or video recommendations, predictive text and game-playing programs that get better the more they are used.

Expert systems compared with machine learning An expert system reasons using rules and facts put in by experts. Machine learning adapts its own processes and data by itself. Both are types of AI.

Deciding if a system is an expert system or machine learning Decide if a system gives advice from a knowledge base and rule base (expert system) or changes its own processes or data (machine learning), then justify with because.

Explaining the basic operation of an AI system Naming the parts of an AI system, what each does, and how they work together to take input, reason on data and rules or learn, and output a result that simulates intelligence.

Writing exam answers about artificial intelligence Use exact key terms (data, rules, reasoning, knowledge base, rule base, inference engine, interface, machine learning) and link each point to a reason.

Just this content description: the 6.3 Artificial Intelligence journey · Add 6.3 Artificial Intelligence to a class →

Printable IGCSE Computer Science Paper 1 Crosswords & Word Searches

Built from the key terms of each block of modules, every one with a full answer key. All free printables →

Crossword: 1.1 Number Systems (Modules 3–17) 10 clues · Number bases: denary, binary and hexadecimal, Denary place values, 16-bit binary place values, Converting 16-bit binary to denary and more

Crossword: 1.1 Number Systems (Modules 18–27) 10 clues · Converting hexadecimal to binary using nibbles, Why hexadecimal is used instead of binary, Where hexadecimal is used in computer science, Binary addition rules and more

Crossword: 1.1 Number Systems and 1.2 Text, Sound and Images (Modules 28–41) 10 clues · Why two's complement is used, The sign bit worth -128, Range of 8-bit two's complement, Converting 8-bit two's complement to denary and more

Crossword: 1.2 Text, Sound and Images and 1.3 Data Storage and Compression (Modules 43–58) 10 clues · Comparing ASCII and Unicode, Analogue sound waves and digital sound, Sample resolution, Effect of sample rate and resolution on accuracy and file size and more

Crossword: 1.3 Data Storage and Compression (Modules 59–68) 10 clues · Kibibyte (KiB), Mebibyte (MiB), Gibibyte (GiB), Tebibyte (TiB) and more

Crossword: 1.3 Data Storage and Compression (Modules 69–84) 10 clues · Converting to a smaller unit, Converting across several units, Giving the answer in the unit asked, Counting the pixels in an image and more

Crossword: 1.3 Data Storage and Compression and 2.1 Data Transmission Types and Methods (Modules 86–109) 10 clues · Why compression is needed: less storage space, Why compression is needed: less bandwidth, Why compression is needed: shorter transmission time, Lossy compression permanently removes data and more

Crossword: 2.1 Data Transmission Types and Methods (Modules 110–120) 10 clues · The three parts of a packet, Packet header, Destination address in a packet header, Originator's address in a packet header and more

Crossword: 2.1 Data Transmission Types and Methods (Modules 121–130) 10 clues · Why packets can take different routes, Packets arriving out of order, Reordering packets at the destination, Describing the packet switching process step by step and more

Crossword: 2.1 Data Transmission Types and Methods (Modules 131–141) 10 clues · Simplex data transmission, Half-duplex data transmission, Full-duplex data transmission, Advantages and disadvantages of simplex, half-duplex and full-duplex and more

Crossword: 2.1 Data Transmission Types and Methods and 2.2 Methods of Error Detection (Modules 142–154) 10 clues · Drawbacks of USB, Evaluating USB for a given use, Why data is checked after transmission, Interference as the cause of transmission errors and more

Crossword: 2.2 Methods of Error Detection (Modules 155–164) 10 clues · Even parity, Odd parity, Working out the parity bit for a byte, Checking a received byte for a parity error and more

Crossword: 2.2 Methods of Error Detection (Modules 168–178) 10 clues · Checksum, Calculating a checksum, Checking a checksum at the receiver, What a checksum can and cannot detect and more

Crossword: 2.2 Methods of Error Detection (Modules 179–188) 10 clues · Bar code check digit, Checking a number with its check digit on entry, What a check digit cannot detect, Automatic repeat query (ARQ) and more

Crossword: 2.2 Methods of Error Detection and 2.3 Encryption (Modules 189–203) 10 clues · Choosing an error detection method for a scenario, Interception of data on a network, Plaintext, Ciphertext and more

Crossword: 2.3 Encryption and 3.1 Computer Architecture (Modules 204–217) 10 clues · Private key, Encrypting with the recipient's public key, Decrypting with the private key, Sending a secure message with asymmetric encryption and more

Crossword: 3.1 Computer Architecture (Modules 218–227) 10 clues · Registers, Program counter (PC), Memory address register (MAR), Memory data register (MDR) and more

Crossword: 3.1 Computer Architecture (Modules 228–239) 10 clues · The fetch-decode-execute cycle, Fetch: sending the address from the PC to the MAR, Fetch: reading the instruction from RAM into the MDR, Fetch: incrementing the PC and copying the instruction to the CIR and more

Crossword: 3.1 Computer Architecture and 3.2 Input and Output Devices (Modules 240–251) 10 clues · Machine code, Embedded system, Devices that use embedded systems, General-purpose computer and more

Crossword: 3.2 Input and Output Devices (Modules 252–261) 9 clues · Barcode scanner, QR code scanner, Barcodes compared with QR codes, Touch screen and more

Crossword: 3.2 Input and Output Devices (Modules 262–272) 10 clues · Choosing a suitable input device for a context, LCD screen, LED screen, Comparing LCD and LED screens and more

Crossword: 3.2 Input and Output Devices (Modules 273–282) 10 clues · 3D printer, Speaker, Actuator, Choosing a suitable output device for a context and more

Crossword: 3.2 Input and Output Devices (Modules 283–292) 10 clues · Humidity sensor, Infra-red sensor, Level sensor, Light sensor and more

Crossword: 3.2 Input and Output Devices and 3.3 Data Storage (Modules 293–303) 10 clues · Sensors, microprocessor and actuator in a control system, Matching sensors to the data they capture, Choosing the most suitable sensor for a given context, Choosing input devices, output devices and sensors together for a system and more

Crossword: 3.3 Data Storage (Modules 304–313) 10 clues · Why secondary storage is needed, Magnetic storage: platters, tracks and sectors, Magnetic storage: reading and writing with electromagnets, Hard disk drive (HDD) and more

Crossword: 3.3 Data Storage (Modules 314–324) 10 clues · Comparing magnetic, optical and solid-state storage, Choosing a secondary storage device for a scenario, Virtual memory, Why virtual memory is needed and more

Crossword: 3.3 Data Storage and 3.4 Network Hardware (Modules 325–341) 10 clues · Comparing cloud storage with local storage, Writing exam answers about data storage, What a MAC address is, MAC addresses are given at manufacture and more

Crossword: 3.4 Network Hardware (Modules 342–354) 7 clues · The limited number of IPv4 addresses, IPv6 address format, Shortening an IPv6 address, Comparing IPv4 and IPv6 and more

Crossword: 3.4 Network Hardware and 4.1 Types of Software and Interrupts (Modules 356–372) 10 clues · Writing exam answers about network hardware and addresses, System software, Examples of application software, System software versus application software and more

Crossword: 4.1 Types of Software and Interrupts (Modules 373–389) 10 clues · OS function: managing files, OS function: providing a graphical user interface (GUI), OS function: providing a command-line interface (CLI), OS function: managing peripherals and drivers and more

Crossword: 4.1 Types of Software and Interrupts (Modules 390–408) 10 clues · Firmware, Bootloader, The start-up sequence of a computer, Layers: applications, operating system, firmware and hardware and more

Crossword: 4.1 Types of Software and Interrupts (Modules 409–418) 10 clues · Classifying an event as a hardware or software interrupt, How an interrupt is generated, The CPU checks for interrupts after each cycle, Interrupt priority and more

Crossword: 4.2 Programming Languages, Translators and IDEs (Modules 419–429) 10 clues · Program and source code, High-level language, Low-level language, Ease of reading and writing code: high-level vs low-level and more

Crossword: 4.2 Programming Languages, Translators and IDEs (Modules 430–439) 10 clues · Assembler, Why translators are needed, Syntax errors and run-time errors reported by translators, Compiler and more

Crossword: 4.2 Programming Languages, Translators and IDEs (Modules 440–449) 10 clues · Advantages of an interpreter, Disadvantages of an interpreter, Comparing a compiler and an interpreter, Interpreter for development, compiler for the final program and more

Crossword: 4.2 Programming Languages, Translators and IDEs and 5.1 The Internet and the World Wide Web (Modules 450–463) 10 clues · IDE function: auto-completion, IDE function: auto-correction, IDE function: prettyprint, Matching an IDE function to a need and more

Crossword: 5.1 The Internet and the World Wide Web (Modules 464–476) 10 clues · URL part: the web page or file name, Splitting a URL into its parts, Purpose of HTTP, HTTP request and response and more

Crossword: 5.1 The Internet and the World Wide Web (Modules 477–489) 10 clues · Browser function: navigation tools, Browser function: storing cookies, Matching a browser function to a need, Why domain names are used instead of IP addresses and more

Crossword: 5.1 The Internet and the World Wide Web and 5.2 Digital Currency (Modules 490–499) 10 clues · Persistent cookies, Comparing session and persistent cookies, Cookie use: saving personal details, Cookie use: tracking user preferences and more

Crossword: 5.2 Digital Currency (Modules 500–509) 10 clues · Digital currency, Digital currency compared with physical cash, Cryptocurrency as an example of digital currency, Digital wallets and more

Crossword: 5.2 Digital Currency (Modules 510–519) 10 clues · Digital ledger, What a ledger record contains, Time-stamp, A record that cannot be altered and more

Crossword: 5.2 Digital Currency and 5.3 Cyber Security (Modules 520–546) 10 clues · Working out ownership from the blockchain, Stopping the same digital currency being spent twice, Writing exam answers about digital currency and blockchain, Trojan horse and more

Crossword: 5.3 Cyber Security and 6.1 Automated Systems (Modules 553–577) 10 clues · Access levels, Anti-spyware software, What a proxy server is, How a proxy server keeps data safe and more

Crossword: 6.1 Automated Systems (Modules 580–607) 10 clues · Feedback in an automated system, Describing how an automated system works, Automated systems in industry, Automated systems in transport and more

Crossword: 6.1 Automated Systems (Modules 608–617) 10 clues · Advantage: accuracy and consistency, Advantage: safety in dangerous places, Advantage: lower running costs and fewer errors, Disadvantage: cost to buy, install and maintain and more

Crossword: 6.1 Automated Systems and 6.2 Robotics (Modules 618–631) 10 clues · Advantages and disadvantages of automation in agriculture, Advantages and disadvantages of automation in weather monitoring, Advantages and disadvantages of automation in gaming, Advantages and disadvantages of automation in lighting and more

Crossword: 6.2 Robotics (Modules 632–641) 10 clues · Characteristic of a robot: programmable, The three characteristics of a robot together, Deciding whether a device is a robot, Example robot: factory equipment and more

Crossword: 6.2 Robotics (Modules 642–651) 10 clues · Role of robots in domestic settings, Role of robots in entertainment, Matching a robot task to its role, Advantage of robots: safer work and more

Crossword: 6.2 Robotics and 6.3 Artificial Intelligence (Modules 652–661) 10 clues · Writing exam answers about robotics, Artificial intelligence (AI), Intelligent behaviour in a computer, The two types of AI in this course and more

Crossword: 6.3 Artificial Intelligence (Modules 662–678) 10 clues · Examples of expert systems, The four parts of an expert system, Knowledge base, Rule base and more

Word Search: 1.1 Number Systems (Modules 3–27) 22 words to find · Number bases: denary, binary and hexadecimal, Denary place values, 16-bit binary place values, Converting 16-bit binary to denary and more

Word Search: 1.1 Number Systems to 1.3 Data Storage and Compression (Modules 28–58) 20 words to find · Why two's complement is used, The sign bit worth -128, Range of 8-bit two's complement, Converting 8-bit two's complement to denary and more

Word Search: 1.3 Data Storage and Compression (Modules 59–84) 20 words to find · Kibibyte (KiB), Mebibyte (MiB), Gibibyte (GiB), Tebibyte (TiB) and more

Word Search: 1.3 Data Storage and Compression and 2.1 Data Transmission Types and Methods (Modules 86–120) 21 words to find · Why compression is needed: less storage space, Why compression is needed: less bandwidth, Why compression is needed: shorter transmission time, Lossy compression permanently removes data and more

Word Search: 2.1 Data Transmission Types and Methods (Modules 121–141) 20 words to find · Why packets can take different routes, Packets arriving out of order, Reordering packets at the destination, Describing the packet switching process step by step and more

Word Search: 2.1 Data Transmission Types and Methods and 2.2 Methods of Error Detection (Modules 142–164) 21 words to find · Drawbacks of USB, Evaluating USB for a given use, Why data is checked after transmission, Interference as the cause of transmission errors and more

Word Search: 2.2 Methods of Error Detection (Modules 168–188) 21 words to find · Checksum, Calculating a checksum, Checking a checksum at the receiver, What a checksum can and cannot detect and more

Word Search: 2.2 Methods of Error Detection to 3.1 Computer Architecture (Modules 189–217) 20 words to find · Choosing an error detection method for a scenario, Interception of data on a network, Plaintext, Ciphertext and more

Word Search: 3.1 Computer Architecture (Modules 218–239) 21 words to find · Registers, Program counter (PC), Memory address register (MAR), Memory data register (MDR) and more

Word Search: 3.1 Computer Architecture and 3.2 Input and Output Devices (Modules 240–261) 22 words to find · Machine code, Embedded system, Devices that use embedded systems, General-purpose computer and more

Word Search: 3.2 Input and Output Devices (Modules 262–282) 22 words to find · Choosing a suitable input device for a context, LCD screen, LED screen, Comparing LCD and LED screens and more

Word Search: 3.2 Input and Output Devices and 3.3 Data Storage (Modules 283–303) 22 words to find · Humidity sensor, Infra-red sensor, Level sensor, Light sensor and more

Word Search: 3.3 Data Storage (Modules 304–324) 20 words to find · Why secondary storage is needed, Magnetic storage: platters, tracks and sectors, Magnetic storage: reading and writing with electromagnets, Hard disk drive (HDD) and more

Word Search: 3.3 Data Storage and 3.4 Network Hardware (Modules 325–354) 20 words to find · Comparing cloud storage with local storage, Writing exam answers about data storage, What a MAC address is, MAC addresses are given at manufacture and more

Word Search: 3.4 Network Hardware and 4.1 Types of Software and Interrupts (Modules 356–389) 20 words to find · Writing exam answers about network hardware and addresses, System software, Examples of application software, System software versus application software and more

Word Search: 4.1 Types of Software and Interrupts (Modules 390–418) 20 words to find · Firmware, Bootloader, The start-up sequence of a computer, Layers: applications, operating system, firmware and hardware and more

Word Search: 4.2 Programming Languages, Translators and IDEs (Modules 419–439) 21 words to find · Program and source code, High-level language, Low-level language, Ease of reading and writing code: high-level vs low-level and more

Word Search: 4.2 Programming Languages, Translators and IDEs and 5.1 The Internet and the World Wide Web (Modules 440–463) 21 words to find · Advantages of an interpreter, Disadvantages of an interpreter, Comparing a compiler and an interpreter, Interpreter for development, compiler for the final program and more

Word Search: 5.1 The Internet and the World Wide Web (Modules 464–489) 21 words to find · URL part: the web page or file name, Splitting a URL into its parts, Purpose of HTTP, HTTP request and response and more

Word Search: 5.1 The Internet and the World Wide Web and 5.2 Digital Currency (Modules 490–509) 20 words to find · Persistent cookies, Comparing session and persistent cookies, Cookie use: saving personal details, Cookie use: tracking user preferences and more

Word Search: 5.2 Digital Currency and 5.3 Cyber Security (Modules 510–546) 21 words to find · Digital ledger, What a ledger record contains, Time-stamp, A record that cannot be altered and more

Word Search: 5.3 Cyber Security and 6.1 Automated Systems (Modules 553–607) 21 words to find · Access levels, Anti-spyware software, What a proxy server is, How a proxy server keeps data safe and more

Word Search: 6.1 Automated Systems and 6.2 Robotics (Modules 608–631) 21 words to find · Advantage: accuracy and consistency, Advantage: safety in dangerous places, Advantage: lower running costs and fewer errors, Disadvantage: cost to buy, install and maintain and more

Word Search: 6.2 Robotics (Modules 632–651) 22 words to find · Characteristic of a robot: programmable, The three characteristics of a robot together, Deciding whether a device is a robot, Example robot: factory equipment and more

Word Search: 6.2 Robotics and 6.3 Artificial Intelligence (Modules 652–678) 20 words to find · Writing exam answers about robotics, Artificial intelligence (AI), Intelligent behaviour in a computer, The two types of AI in this course and more

Journeys using these modules

IGCSE Computer Science 0478 — 1.1 Number Systems, IGCSE Computer Science 0478 — 1.2 Text, Sound and Images, IGCSE Computer Science 0478 — 1.3 Data Storage and Compression, IGCSE Computer Science 0478 — 2.1 Data Transmission Types and Methods, IGCSE Computer Science 0478 — 2.2 Methods of Error Detection, IGCSE Computer Science 0478 — 2.3 Encryption, IGCSE Computer Science 0478 — 3.1 Computer Architecture, IGCSE Computer Science 0478 — 3.2 Input and Output Devices, IGCSE Computer Science 0478 — 3.3 Data Storage, IGCSE Computer Science 0478 — 3.4 Network Hardware, IGCSE Computer Science 0478 — 4.1 Types of Software and Interrupts, IGCSE Computer Science 0478 — 4.2 Programming Languages, Translators and IDEs, IGCSE Computer Science 0478 — 5.1 The Internet and the World Wide Web, IGCSE Computer Science 0478 — 5.2 Digital Currency, IGCSE Computer Science 0478 — 5.3 Cyber Security, IGCSE Computer Science 0478 — 6.1 Automated Systems, IGCSE Computer Science 0478 — 6.2 Robotics, IGCSE Computer Science 0478 — 6.3 Artificial Intelligence, IGCSE Computer Science 0478 — 7a Program Development Life Cycle, ACARA Digital Technologies Years 7–8 — Hardware and Performance, ACARA Digital Technologies Years 7–8 — Wired and Wireless Networks, ACARA Digital Technologies Years 7–8 — Representing Text, Images and Sound, ACARA Digital Technologies Years 7–8 — Binary Number Representation, ACARA Digital Technologies Years 7–8 — Acquiring and Storing Data, ACARA Digital Technologies Years 7–8 — Networks and Cyber Threats, ACARA Digital Technologies Years 9–10 — Networked Systems and Access Control, ACARA Digital Technologies Years 9–10 — Data Compression, ACARA Digital Technologies Years 9–10 — Acquiring and Validating Data, ACARA Digital Technologies Years 9–10 — Cyber Security Threats and Vulnerabilities, QCE Digital Solutions Unit 1 — Understanding Digital Problems, QCE Digital Solutions Unit 1 — Algorithms and Programming Techniques, QCE Digital Solutions Unit 1 — Programmed Solutions, QCE Digital Solutions Unit 2 — Data and Programming Techniques, QCE Digital Solutions Unit 3 — Interactions Between Users, Data and Digital Systems, QCE Digital Solutions Unit 4 — Digital Methods for Exchanging Data, QCE Digital Solutions Unit 4 — Complex Digital Data Exchange Problems and Solution Requirements, QCE Digital Solutions Unit 4 — Prototype Digital Data Exchanges, WA Computer Science ATAR Year 11 — Network Communications, WA Computer Science ATAR Year 11 — Cyber Security

Or build your own Journey from any of these modules →

Frequently Asked Questions

Are these worksheets free?

Yes — every worksheet and its answer key is free to view, download, and print, with no account required to access any individual module.

Do I need an account?

No account is needed to view or print a worksheet. A free teacher account adds extras like assigning modules to a class and tracking progress automatically — it takes under three minutes to set up and doesn't need a credit card.

What year level is this for?

This curriculum is aligned to the Australian Curriculum (ACARA) and Victorian Curriculum, spanning roughly Years 3 to 10 — from first sequencing and variables through to object-oriented programming and advanced data structures. Start wherever matches your class's current level; each module builds on the last.

Can I print them?

Yes — every module has a one-click Print Worksheet button that generates a printable page with the practice questions and a full answer key.

Is this aligned to a curriculum?

Yes — the module sequence is mapped to the Australian Curriculum (ACARA) and Victorian Curriculum, and a class's progress is reported back against those curriculum bands (e.g. ACARA Years 5–6 sequencing and iteration, Years 7–8 functions and data structures), not just a generic difficulty scale.

Can students use this without a teacher?

Yes — students can start any module and practice directly, no class or account required. Joining a teacher's class with a class code adds progress tracking, class badges, and live Sprints, but isn't needed to work through the worksheets or modules solo.

Do I need to know IGCSE Computer Science Paper 1 myself to teach this?

No — every module comes with a full worked answer key, and Cloodit tracks who's stuck automatically, so you don't need to solve each exercise yourself before assigning it or be able to debug a student's work line by line.

Cloodit turns curriculum-aligned coding content into journeys students work through one biome at a time.

The 'Seahorse' badge — Range Rider, one of Cloodit's 106 collectible badges

Students earn collectable badges

Over 100 of them, across seven natural biomes.

Study Buddy

Students build a real study resource

Turns their work into revision material ready for Flash Cards and Exam study.

Diamond Dash — one of Cloodit's live, competitive Sprint games

Students lock in with Sprints

Live, competitive practice for the start of the lesson or a teacher-led lesson finisher.

A Cloodit certificate of achievement, ready to personalise and print

Custom printable certificates

Honour your top performers, or encourage a student who's trying hard — ready to print in seconds.

Add to class →

For Teachers

Set this curriculum for your class and see who needs help, automatically.

Create a free teacher account →

No credit card. No setup fee. Make a class and invite students in under three minutes.

For Students

Practice this topic interactively, track progress, and unlock badges.

Start Learning Free →

Have a class code?