KS3 Computing key terms

108 terms with short definitions you can learn for the exam. Type to filter the list.

Key terms 91

Abstraction: Removing unnecessary detail from a problem so you can focus on what matters. A map of the Underground is an abstraction.
Algorithm: A precise set of step-by-step instructions to solve a problem or complete a task.
ALU (arithmetic logic unit): The part of the CPU that does calculations and logic comparisons.
AND: A Boolean operator that gives True (1) only when both inputs are True.
Application software: Programs that help a user do a task, such as a word processor, web browser or game.
ASCII: A character set that uses 7 bits to give codes to 128 characters, including English letters, digits and symbols. A is 65.
Binary: A number system that uses only two digits, 0 and 1. Computers store all data in binary.
Binary search: A search that checks the middle item of a sorted list, then throws away the half that cannot hold the target, again and again.
Bit: A binary digit: a single 0 or 1. The smallest unit of data.
Bit depth: The number of bits used to store each sound sample. More bits give a more accurate recording.
Boolean: A data type with only two values: True or False.
Brute force attack: Trying every possible password until the right one is found. Long passwords make this take far longer.
Bubble sort: A sort that compares neighbouring pairs and swaps them if they are in the wrong order, making passes until no swaps are needed.
Bug: An error in a program that stops it working as intended.
Byte: A group of 8 bits.
Cache: A small amount of very fast memory close to the CPU that holds often-used instructions and data.
Character set: A list of characters and the binary code a computer uses for each one, such as ASCII or Unicode.
Clock speed: How many fetch-decode-execute cycles a CPU can do each second, measured in hertz. 3 GHz is 3 billion cycles per second.
Colour depth: The number of bits used to store the colour of each pixel. n bits give 2^{n} possible colours.
Computational thinking: Solving problems in a way a computer could carry out, using decomposition, pattern recognition, abstraction and algorithms.
Condition: An expression that is either True or False, such as score > 50, used in if statements and while loops.
Control unit (CU): The part of the CPU that decodes instructions and controls the other parts.
CPU (central processing unit): The processor: the part of a computer that fetches, decodes and executes the instructions of a program.
Cyberbullying: Using technology, such as messages or social media, to upset, threaten or embarrass someone, often repeatedly.
Data type: The kind of data a value is, such as integer, real (float), string or Boolean.
Debugging: Finding and fixing errors in a program.
Decomposition: Breaking a big problem down into smaller problems that are easier to solve.
Denary: The base 10 number system we use every day, with the digits 0 to 9.
Digital artefact: Something made with digital technology, such as a website, video, presentation, app or animation.
Digital footprint: The trail of information about you online, from what you and other people post, like and share.
DNS (domain name system): The system that turns a web address, such as gov.uk, into the IP address of the server.
Elif: Short for "else if" in Python: it checks another condition when the ones before it were False.
Fetch-decode-execute cycle: What the CPU repeats for every instruction: fetch it from memory, decode it, then carry it out.
Firewall: Software or hardware that checks data coming into and going out of a network and blocks anything not allowed.
Flowchart: A diagram of an algorithm that uses shapes such as ovals, rectangles, diamonds and parallelograms joined by arrows.
For loop: A count-controlled loop that repeats a set number of times.
Function: A subprogram that carries out a task and returns a value to the code that called it.
Hardware: The physical parts of a computer system that you can touch, such as the CPU, keyboard and screen.
Index (list): The position number of an item in a list. In Python the first index is 0.
Infinite loop: A loop that never stops because its condition never becomes False.
Input: Data put into a computer, for example from a keyboard, mouse, microphone or sensor.
Integer: A whole number data type, such as 7 or −3.
Internet: A worldwide network of networks. It is the hardware: cables, routers and connected computers.
IP address: A unique number that identifies a device on a network so data can be sent to it.
Iteration: Repeating a set of instructions, using a loop.
Kilobyte (KB): 1,000 bytes. (A kibibyte, KiB, is 1,024 bytes.)
LAN (local area network): A network covering a small area, such as a home, school or office.
Linear search: A search that checks each item in a list in turn, from the start, until the target is found or the list ends.
List: A data structure that stores many items under one name, in order, such as scores = [4, 7, 2].
Logic gate: A tiny electronic circuit that takes binary inputs and gives one binary output, such as an AND, OR or NOT gate.
Malware: Malicious software made to harm a computer or steal data, such as viruses, worms, spyware and ransomware.
Merge sort: A divide and conquer sort that splits a list into single items, then merges them back together in order.
Metadata: Data about data, such as an image's width, height and the date it was taken.
Model: A program or simulation that represents a real-world system, keeping only the important details.
Nibble: A group of 4 bits: half a byte.
NOT: A Boolean operator that flips its input: True becomes False and False becomes True.
Operating system: System software that runs the computer: it manages memory, files, hardware and the user interface. Examples: Windows, macOS, Android.
OR: A Boolean operator that gives True (1) when at least one input is True.
Output: Information sent out from a computer, for example to a screen, speaker or printer.
Overflow: An error when the result of a calculation needs more bits than are available, such as an 8-bit sum above 255.
Packet: A small piece of data sent across a network, with the address it is going to and where it fits in the whole message.
Parameter: A variable in a subprogram's definition that receives a value when the subprogram is called.
Pattern recognition: Spotting things that are the same or similar in different problems, so one solution can be reused.
Phishing: Fake messages or websites that pretend to be from someone trusted to trick you into giving away passwords or personal details.
Pixel: Short for picture element: one tiny dot of colour in a bitmap image.
Procedure: A subprogram that carries out a task but does not return a value.
Program: A set of instructions written in a programming language that a computer can run.
RAM (random access memory): Main memory that holds the programs and data in use right now. It is volatile: it loses its contents when the power goes off.
Real (float): A data type for numbers with a decimal part, such as 3.75.
Resolution: The number of pixels in an image, given as width × height, such as 1920 × 1080.
ROM (read-only memory): Memory that keeps its contents when the power is off. It holds the instructions a computer needs to start up.
Router: A device that sends packets of data between networks, choosing where each one goes next.
Sample rate: How many sound samples are taken each second, measured in hertz (Hz). CD audio uses 44,100 Hz.
Secondary storage: Long-term storage that keeps files when the power is off, such as a hard disk drive, SSD or USB stick.
Selection: Choosing which code to run depending on a condition, using if, elif and else.
Sequence: Instructions carried out one after another, in order.
Software: The programs that run on a computer. It is not physical.
Spreadsheet: A program that stores data in a grid of cells and calculates with formulas, such as =SUM(B2:B6).
String: A data type for text, written in quotation marks, such as "hello".
Subprogram: A named block of code that can be called from elsewhere in a program: a procedure or a function.
Syntax error: A mistake in the rules of the language, such as a missing colon or bracket, so the program cannot run.
System software: Software that runs the computer itself, such as the operating system and utility programs.
Trace table: A table that records the value of each variable, line by line, as you work through a program by hand.
Truth table: A table showing the output of a logic gate or Boolean expression for every possible combination of inputs.
Two-step verification: Logging in with a password plus a second check, such as a code sent to your phone. Also called two-factor authentication.
Unicode: A large character set that covers the letters of many languages, symbols and emoji. It uses more bits per character than ASCII.
Variable: A named store in memory that holds a value, which can change while the program runs.
Volatile: Describes memory that loses its contents when the power is turned off, such as RAM.
WAN (wide area network): A network covering a large area, such as a country or the world. The internet is the biggest WAN.
While loop: A condition-controlled loop that repeats while its condition is True.
World Wide Web: The collection of web pages and websites, linked together, that you reach through the internet using a browser.

Formulas and facts to know 17

Arithmetic operators in Python: + add, − subtract (typed as -), * multiply, / divide, // whole-number division, % remainder (modulus).
ASCII codes to know: A = 65, B = 66 ... Z = 90. a = 97, b = 98 ... z = 122. The digit 0 = 48. Lower case = upper case + 32.
Binary addition rules: 0 + 0 = 0. 0 + 1 = 1. 1 + 1 = 0 carry 1. 1 + 1 + 1 = 1 carry 1.
Binary place values (8 bits): 128, 64, 32, 16, 8, 4, 2, 1. Each column is worth double the one to its right.
Binary units: 1 kibibyte (KiB) = 1,024 bytes. 1 mebibyte (MiB) = 1,024 KiB. 1 gibibyte (GiB) = 1,024 MiB. Use whichever units a question asks for.
Clock speed: 1 Hz = 1 cycle per second. 1 MHz = 1 million. 1 GHz = 1 billion cycles per second.
Comparison operators in Python: == equal to, != not equal to, < less than, > greater than, <= less than or equal to, >= greater than or equal to.
Converting units: Going to a smaller unit, multiply (2 bytes = 2 × 8 = 16 bits). Going to a bigger unit, divide (4000 bytes = 4000 ÷ 1000 = 4 KB).
Flowchart symbols: Oval (rounded box): start or stop. Rectangle: process. Diamond: decision (yes or no). Parallelogram: input or output.
Image file size: File size in bits = width × height × colour depth. Divide by 8 for bytes.
Logic gates: AND: 1 only if both inputs are 1. OR: 1 if at least one input is 1. NOT: flips 0 to 1 and 1 to 0.
Number of colours: Colours = 2^{colour depth}. 1 bit: 2 colours, 8 bits: 256 colours, 24 bits: 16,777,216 colours.
Range of n bits: n bits can store 2^{n} different values. 8 bits store 256 values: 0 to 255.
range() in Python: range(5) gives 0, 1, 2, 3, 4. range(1, 6) gives 1 to 5. range(0, 10, 2) gives 0, 2, 4, 6, 8. It stops one before the end number.
Sound file size: File size in bits = sample rate × bit depth × length in seconds (for one channel, mono). Divide by 8 for bytes.
Spreadsheet functions: =SUM(B2:B6) adds, =AVERAGE(B2:B6) finds the mean, =MAX(B2:B6) and =MIN(B2:B6) find the largest and smallest. Every formula starts with =.
Units of data: 1 nibble = 4 bits. 1 byte = 8 bits. 1 kilobyte (KB) = 1,000 bytes. 1 megabyte (MB) = 1,000 KB. 1 gigabyte (GB) = 1,000 MB. 1 terabyte (TB) = 1,000 GB.

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