← Years 5–6 Digital Systems

Central processing unit (CPU)

The central processing unit is the 'brain' of a digital system. It carries out program instructions one after another and processes data. Its speed affects how fast tasks run.

Part of: 5-6 Digital Technologies Vic Curric - Digital Systems & Security — Module 8, 7-8 Digital Technologies Vic Curric - Digital Systems and Security — Module 3, IGCSE Computer Science 0478 — 3.1 Computer Architecture — Module 2, IGCSE Computer Science 0478 — 4.1 Types of Software and Interrupts — Module 41, ACARA Digital Technologies Years 5–6 — Inside Digital Systems — Module 6, ACARA Digital Technologies Years 7–8 — Hardware and Performance — Module 9

Understanding Central processing unit (CPU) in Years 5–6 Digital Systems

What it does: The CPU repeats this cycle for each instruction: fetch it, work out what it means, then carry it out, before moving on to the next one. Data comes in from an input device, the CPU processes it by following program instructions, and the result goes out to an output device. The CPU is often called the 'brain' because it does the thinking and processing. Showing pictures is the job of an output device like a monitor. A CPU follows program instructions in order, one after another. It does not guess or skip them. Processing speed affects how fast tasks run. Storing photos depends on storage devices, not the CPU speed.

Common mistakes: A for loop line must end with a colon. The CPU works through each step one after another, so the loop line should be: for s in steps:. Python is case sensitive, so Print with a capital P does not exist. It should be print("Time taken:", time).

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Learning
Duo
Which part of a digital system carries out program instructions and processes data?
The monitorThe CPU
Matches
The CPU is where all files are kept permanently
↓
The CPU does not store files. It processes data and runs instructions. Storage devices such as a hard drive or SSD keep files permanently.
Applying
Meanings
Term
CPU
Meaning
The central processing unit is the 'brain' of a digital system. It carries out program instructions one after another and processes data. Its speed affects how fast tasks run.
Practice
CPU = the brain of the system
Testing
Gaps
The is the brain of the system
Check Answer
Spots
1steps = ["add", "save"]
2for s in steps

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Quick Questions

1. Which part of a digital system carries out program instructions and processes data?
A. The CPU ✓
B. The monitor
The CPU (central processing unit) is the 'brain' of the system. It carries out instructions and processes data. A monitor only displays output.
2. Which description of the CPU is correct?
A. It is the screen that shows pictures
B. It is the 'brain' of a digital system ✓
The CPU is often called the 'brain' because it does the thinking and processing. Showing pictures is the job of an output device like a monitor.
3. How does a CPU work through a program?
A. It ignores the instructions and guesses
B. It follows instructions one after another ✓
A CPU follows program instructions in order, one after another. It does not guess or skip them.
4. A faster CPU usually means a computer will...
A. Run tasks more quickly ✓
B. Store more photos permanently
Processing speed affects how fast tasks run. Storing photos depends on storage devices, not the CPU speed.
5. True or false: The CPU processes data.
A. True ✓
B. False
True. Processing data is one of the main jobs of the CPU, along with carrying out program instructions.

Match the Pairs

CPU → The central processing unit, the 'brain' of a digital system that carries out program instructions and processes data
3.5 GHz → A measure of CPU processing speed: how many cycles it can run each second
The CPU follows instructions one after another, in order → fetch -> decode -> execute
The CPU processes data in the input, process, output flow → input -> CPU -> output
The CPU is where all files are kept permanently → The CPU does not store files. It processes data and runs instructions. Storage devices such as a hard drive or SSD keep files permanently.
A slower CPU makes tasks run faster → A faster CPU speed means tasks run faster. A slower CPU takes longer to carry out instructions.

Key Term

CPU
The central processing unit is the 'brain' of a digital system. It carries out program instructions one after another and processes data. Its speed affects how fast tasks run.

Fill in the Blanks

1. The CPU is the brain of the system
Hint: Type the abbreviation for the component that acts as the brain of a digital system.
2. instructions = ["add", "save", "show"] CPU.run(instructions[0])
Hint: Type the index number of the first instruction in the list, since the CPU starts at the beginning.
3. for instruction in program: CPU.run(instruction)
Hint: Type the keyword that repeats a step for each instruction, one after another.
4. isFast = cpuSpeed > 2.0
Hint: Type the comparison operator that checks whether the CPU speed is greater than the number.
5. result = CPU.process(data)
Hint: Type the method name for the CPU working on data.

Spot the Error

Question 1
A steps = ["add", "save"]
B for s in steps
C print("CPU runs", s)
Line B — A for loop line must end with a colon. The CPU works through each step one after another, so the loop line should be: for s in steps:
Question 2
A speed = 2
B tasks = 8
C time = tasks / speed
D Print("Time taken:", time)
Line D — Python is case sensitive, so Print with a capital P does not exist. It should be print("Time taken:", time).
Question 3
A speed = 4
B work = 12
C time = work * speed
D print("Seconds:", time)
Line C — A faster CPU finishes work in less time, so time must be work divided by speed. It should be time = work / speed, not multiplied.
Question 4
A step == 1
B while step <= 3:
C print("Run step", step)
D step = step + 1
Line A — A single = stores a value in a variable, but == only compares values. To set the starting step, write step = 1.
Question 5
A number = 5
B doubled = number / 2
C print("Result:", doubled)
Line B — The CPU processes data using instructions. Dividing by 2 halves the number instead of doubling it. It should be doubled = number * 2.

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