ACARA Digital Technologies Years 5–6 — Representing Data with Numbers Hangman

The 36 key terms

1digital data

Computers store text, pictures and sound as numbers. Data is converted into number codes so a digital system can store it and work with it.

2file

A named chunk of stored data. Pictures, sounds and videos are all data that a digital system saves as files, such as photo.jpg, song.mp3 or clip.mp4.

3binary

Using only two values, like 0 and 1 or on and off. Computers store all data using just these two states.

4bit

A bit is a single binary digit that is either 0 or 1, like a switch that is off (0) or on (1). A group of 8 bits is called a byte.

50 = off, 1 = on

A switch has two states. We write 0 for off and 1 for on, so a row of switches or LEDs can be written as binary digits, like 1 0 1 1.

6encode / decode

To encode is to turn information into a code. To decode is to turn the code back into the information, using a key. They are opposites.

8pixel

A pixel is one tiny square in a grid that makes up a digital image. Each pixel is stored as a number, such as 0 for white or 1 for black.

9row by row

Read a pixel grid in order: start at the top row, go left to right across it, then move down to the next row until the grid ends.

101 = black, 0 = white

To encode a black-and-white picture, write 1 for each black pixel and 0 for each white pixel. Work row by row, one bit per pixel.

11decode

To turn a code back into a picture: fill the grid row by row, colouring a square for each 1 and leaving it white for each 0. Then check the picture makes sense.

12decode to check

One wrong digit in an image code changes just one pixel. Decode the code back into a picture to spot the wrong pixel, then fix that digit.

13pattern

Something that repeats or mirrors in an image code, like matching rows, a symmetrical picture or a run of the same digit. You can spot it and describe it in words.

14run-length encoding

Compress a black-and-white image by writing each row as counts of same-coloured pixels in a run, starting with white. Row 00000 111 00 becomes 5,3,2. Counts can rebuild the grid.

15run-length decoding

Turn counts back into pixels: write that many of one colour, then that many of the other, taking turns, until the row is full. Start with white. A first count of 0 means the row starts black.

171 bit = 2 colours

One bit per pixel can only be 0 or 1, so each pixel can only be one of two colours, like black and white. A photo needs many more colours, so it needs more bits.

192^bits

Each extra bit doubles the colours a pixel can show: 1 bit gives 2, 2 bits give 4 and 3 bits give 8. So the number of colours is 2 times itself, once for each bit.

20colour key

A list that matches each whole number to a colour, like 1 = red, 2 = blue and 3 = yellow, so a grid of numbers can show a picture.

23spreadsheet

A grid of columns (letters, running down) and rows (numbers, running across). A cell is where a column and row meet, like B3. Each worksheet holds one grid.

25Click a cell, type, press Enter

To store data, click a cell, type your value, then press Enter to save it. Tab saves it and moves right. Text lines up left and numbers line up right.

26fill colour

A spreadsheet tool that changes the background colour of the selected cell or cells. Click one cell or drag over a block, then pick a colour. Choose No fill to remove the colour.

27column width = row height

Set the column width and row height to the same size so each cell is a square. A block of square cells then looks like a pixel grid.

28Ctrl+C, Ctrl+V, Ctrl+Z

Keyboard shortcuts that copy, paste and undo faster than using menus. Ctrl+X cuts, Ctrl+S saves and Ctrl+F finds. On a Mac, press Cmd instead of Ctrl.

29conditional formatting

A rule that colours a cell by itself when its number matches a condition, like a cell equal to 1 turning yellow. Change the number and the colour changes too.

30Add new rule

Each extra conditional formatting rule links one more number to one more colour, so one grid of numbers can show many colours.

32pixel art

A picture made of coloured squares. In a spreadsheet, you type a whole-number colour code in each cell and formatting rules turn each number into its colour.

33character code

A number the computer uses to stand for one letter or symbol. It stores the number, then turns it back into the character on screen. In one A=1 code, A is 1 and B is 2.

34encode

To encode a word, swap each letter for its number in the code, so with A=1, B=2 and C=3, CAB becomes 3 1 2. To decode it, swap each number back for its letter.

35binary code

A pattern of 0s and 1s, like a thread of two bead colours. Every letter has its own pattern, so a computer can store text as 0s and 1s.

36data type

The kind of data a value is, such as a number, text or true/false. The data type decides what the computer can do with the value.

37whole number

A number with no fraction or decimal part, like 0, 7 or 250. We use whole numbers to count things, such as scores, lives or students. 3.5 is not a whole number.

38numeric data vs text data

Numeric data is numbers you can calculate with, like 12 or 3.5. Text data is words and characters, like cat or a phone number, which you never add up or average.

39string

A string is text: a row of characters such as letters, digits, symbols and spaces, written inside quote marks like "cat". Even "5" is a string.

40Boolean

A data type with only two possible values: true or false. It stores the answer to a yes/no question, like 'is the light on?', just like on and off in binary.

44concatenation

Gluing two pieces of text end to end into one, so "sun" and "shine" make "sunshine". It joins text together; it does not add numbers, so "3" and "4" make "34".

47choose a data type

Ask what you will do with the value: calculate with it (number), join or show it (text), or answer yes/no (true/false). A phone number is text because you never add it.

48A computer stores a picture as numbers

Digital systems turn pictures, colours and text into numbers. Binary uses only 0 and 1, like off and on, and the data type decides what you can do with it.