Year 7 Computer Science

Algorithms

What is an Algorithm?

An algorithm is a precise, step-by-step set of instructions for solving a problem
A good algorithm: works for all valid inputs, terminates (doesn't run forever), produces the correct output
Algorithms can be expressed as pseudocode, flowcharts, or plain English

Flowcharts

Oval: start/end (terminal) | Rectangle: process (action) | Diamond: decision (question with yes/no)
Parallelogram: input/output | Arrows show the flow of control

Three Types of Programming Structure

Sequence: instructions execute in order, one after another
Selection (IF statements): choose between two or more paths based on a condition
Iteration (loops): repeat instructions. Two main types: count-controlled (for loop) and condition-controlled (while loop)

Searching Algorithms

Linear search: check each item one by one from start to finish. Works on any list. Can be slow for large lists (worst case: check all items)
Binary search: requires a sorted list. Check the middle item; if the target is smaller, search the left half; if larger, search the right half. Repeat. Much faster for large lists

Sorting Algorithms

Bubble sort: compare adjacent pairs; swap if out of order; repeat passes until no swaps needed. Simple but slow for large lists
Merge sort: split list in half repeatedly, sort each half, then merge them back together. Faster for large lists

Programming Basics

Key Programming Concepts

Variable: a named location in memory that stores a value (can change). e.g. score = 0
Constant: like a variable, but its value cannot change. e.g. MAX_LIVES = 3
Data type: the type of value stored. Common types: integer (whole number), float/real (decimal number), string (text), Boolean (True or False)
Input: data entered by the user. e.g. name = input("Enter your name: ")
Output: data displayed to the user. e.g. print("Hello")
Operator: performs a calculation. Arithmetic: + − × / // (integer division) % (modulo/remainder)
Comparison operators: == (equal to) != (not equal) > < >= <=
Logical operators: AND, OR, NOT

Selection (IF Statements)

Python Example score = int(input("Enter score: ")) if score >= 70: print("Pass") elif score >= 50: print("Near pass") else: print("Fail")

Iteration (Loops)

FOR loop (count-controlled): repeats a fixed number of times
WHILE loop (condition-controlled): repeats as long as a condition is True

For Loop Example for i in range(1, 6): print(i) # Prints 1, 2, 3, 4, 5 While Loop Example password = "" while password != "secret": password = input("Enter password: ") print("Access granted")

Subprograms (Functions and Procedures)

A function / procedure is a named block of code that can be called multiple times
Reduces repetition (DRY principle: Don't Repeat Yourself)
Functions return a value; procedures do not

Binary & Data Representation

Binary (Base 2)

Computers use binary (0s and 1s) because electronic circuits have two states: off (0) and on (1)
A bit (binary digit) is the smallest unit: 0 or 1
A byte = 8 bits
1 KB (kilobyte) ≈ 1000 bytes; 1 MB ≈ 1,000,000 bytes; 1 GB ≈ 1,000,000,000 bytes

Binary Column Values

128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 (powers of 2, from left to right)
To convert decimal to binary: find which powers of 2 add up to the number
e.g. 75 = 64 + 8 + 2 + 1 = 01001011 in binary
To convert binary to decimal: multiply each bit by its column value and add
e.g. 10110101 = 128+32+16+4+1 = 181

Adding Binary Numbers

0 + 0 = 0 | 0 + 1 = 1 | 1 + 0 = 1 | 1 + 1 = 10 (carry 1)
1 + 1 + 1 = 11 (write 1, carry 1)

Hexadecimal (Base 16)

Hex digits: 0 1 2 3 4 5 6 7 8 9 A B C D E F (A=10, B=11, C=12, D=13, E=14, F=15)
Used in computing because each hex digit represents exactly 4 binary digits (a nibble)
e.g. hex FF = 1111 1111 in binary = 255 in decimal
Used in: web colours (#FF5733), MAC addresses, memory addresses

Data Types & Storage

Text (Character Encoding)

ASCII: 7-bit code; represents 128 characters (letters, digits, punctuation)
e.g. 'A' = 65, 'a' = 97, '0' = 48
Unicode: extended system that covers all world languages; UTF-8 most common
Unicode uses more bits, allowing over 1 million characters

Images

A bitmap image is made of pixels (picture elements)
Each pixel stores colour data as binary
Colour depth: the number of bits used per pixel. 1 bit = 2 colours; 8 bits = 256 colours; 24 bits = 16.7 million colours
Image file size (bits) = width × height × colour depth
Higher resolution (more pixels) = larger file size, more detail

Sound

Analogue sound is converted to digital using Analogue-to-Digital Converter (ADC)
Sample rate: how many times per second the sound is measured (Hz). Higher = better quality
Sample resolution (bit depth): how many bits used per sample. Higher = more precise
Sound file size = sample rate × sample resolution × duration (seconds) × channels

Data Compression

Compression reduces file size for faster transmission and less storage
Lossy compression: removes some data permanently; quality is slightly reduced (MP3 for audio, JPEG for images)
Lossless compression: no data is lost; the original can be perfectly restored (PNG, ZIP)

Hardware & Software

Inside a Computer

CPU (Central Processing Unit): the "brain" — fetches, decodes, and executes instructions
RAM (Random Access Memory): temporary memory; holds currently running programs and data; lost when power off
ROM (Read Only Memory): permanent memory; holds the boot instructions (BIOS/UEFI); not lost when power off
Hard disk drive (HDD) / Solid state drive (SSD): permanent secondary storage for files, programs, OS
Motherboard: the main circuit board; connects all components
GPU (Graphics Processing Unit): handles graphics and display rendering
Power supply unit (PSU): converts mains electricity to DC for components

Input and Output Devices

Input devices: keyboard, mouse, touchscreen, microphone, scanner, webcam, barcode reader
Output devices: monitor, printer, speakers, headphones, projector
Some devices are both input and output: touchscreen, headphones with microphone

Software

System software: manages the hardware and provides a platform for other software. Includes: operating system (OS), device drivers, utilities
Application software: designed for a specific user task. Includes: word processors, web browsers, games, email clients
Operating system (OS): manages memory, runs programs, handles file management, provides user interface. Examples: Windows, macOS, Linux, Android, iOS

Networks & the Internet

Types of Network

LAN (Local Area Network): covers a small area (home, school, office); connected by cables or Wi-Fi; owned by the organisation
WAN (Wide Area Network): covers a large area (country, world); the Internet is the world's largest WAN; uses leased telephone lines and satellites

Network Hardware

Router: directs data packets between networks; connects a LAN to the Internet
Switch: connects devices within a LAN; sends data only to the intended device
Network Interface Card (NIC): hardware in a device that enables network connection
Wireless Access Point (WAP): allows devices to connect via Wi-Fi
Modem: converts digital data to analogue signals (for transmission over telephone lines) and back

Network Topologies

Star topology: all devices connect to a central switch/hub. Reliable (if one device fails, others work); fast; expensive
Bus topology: all devices share one cable. Cheaper; if the cable fails, whole network fails
Ring topology: devices connected in a circle. Each device has exactly two connections

Protocols

A protocol is an agreed set of rules for how data is transmitted
TCP/IP: the fundamental protocol suite of the Internet; breaks data into packets and reassembles them
HTTP: used to request web pages (HyperText Transfer Protocol)
HTTPS: secure version of HTTP; data is encrypted using SSL/TLS
FTP: File Transfer Protocol; used to transfer files between computers
SMTP/POP3/IMAP: used for sending and receiving email
DNS (Domain Name System): translates domain names (e.g. google.com) into IP addresses

E-Safety & Cybersecurity

Staying Safe Online

Use strong, unique passwords for each account. A strong password is long, mixes letters/numbers/symbols, and doesn't use personal information
Enable two-factor authentication (2FA) where possible
Never share personal information (full name, address, school, photos) with strangers online
Recognise phishing emails: urgent language, poor spelling, suspicious links — do NOT click unknown links
Only download software from trusted sources
Use privacy settings on social media to control who sees your information
If you see something that worries you online, tell a trusted adult

Types of Cybercrime and Threats

Malware: malicious software. Types include: virus (spreads and damages files), worm (spreads itself across networks), Trojan (looks legitimate but is harmful), ransomware (encrypts files and demands payment), spyware (records user activity secretly)
Phishing: fake emails/websites pretending to be trusted organisations to steal login details or financial information
Hacking: gaining unauthorised access to computer systems
Social engineering: manipulating people into giving away sensitive information
DDoS attack: overwhelming a server with traffic so it cannot function

Protection

Antivirus software: detects and removes malware
Firewall: monitors and controls incoming/outgoing network traffic based on rules
Encryption: scrambles data so only authorised users can read it
Regular updates and patches: fix security vulnerabilities in software
Backup: keeping copies of data in case of data loss from attack or hardware failure

Digital Wellbeing

Screen time: balance screen use with offline activities, sleep, and face-to-face interaction
Cyberbullying: bullying that takes place through digital technology. If experienced: keep evidence, block the bully, tell a trusted adult, report to the platform
Online gaming: be careful about in-game purchases, stranger contact, and excessive play time
Copyright: using someone else's work (images, music, code) without permission may be illegal
Digital footprint: everything you do online can leave a permanent record — think before you post

💻 Year 7 Computer Science