Year 8 Computer Science

Functions & Procedures

Why Use Subprograms?

Break complex programs into smaller, manageable chunks
Avoid repeating code (DRY: Don't Repeat Yourself)
Easier to test, debug, and maintain
Can be reused in different parts of the same program or in other programs

Procedures vs Functions

Procedure: a named block of code that performs an action; does NOT return a value
Function: a named block of code that performs an action AND returns a value

Python Examples # Procedure (no return value) def greet(name): print("Hello, " + name) greet("Alice") # Output: Hello, Alice # Function (returns a value) def add(a, b): return a + b result = add(3, 5) # result = 8

Parameters and Arguments

Parameter: the variable in the function definition that receives a value
Argument: the actual value passed in when the function is called
A function can have multiple parameters separated by commas
Default parameter values: def greet(name="World") — if no argument given, "World" is used

Scope

Local variable: defined inside a function; can only be used inside that function
Global variable: defined outside any function; accessible throughout the program
Using global variables inside functions: use the global keyword in Python, or pass variables as parameters (preferred approach)

Lists, Files & String Manipulation

Lists (Arrays)

A list (called an array in most languages) stores multiple values in a single variable
Created with square brackets: fruits = ["apple", "banana", "cherry"]
Indexing: starts at 0. fruits[0] = "apple"; fruits[2] = "cherry"
Negative indexing: fruits[−1] = the last item ("cherry")
Key operations: append (add to end), remove, insert, sort, len (length), range
Iterating: for fruit in fruits: print(fruit)
List slicing: fruits[1:3] = ["banana", "cherry"] (from index 1 up to but not including index 3)

String Manipulation

Strings are sequences of characters; accessed like lists using indices
Concatenation: "Hello" + " " + "World" = "Hello World"
String methods: .upper(), .lower(), .strip() (remove whitespace), .replace(), .split()
.find() returns the index of a substring; returns −1 if not found
len("Hello") = 5 (number of characters)
f-strings: name = "Alice"; print(f"Hello, {name}!") → "Hello, Alice!"

File Handling

Programs can read and write data to text files for persistence
Open a file: file = open("data.txt", "r") — "r" = read; "w" = write (overwrites); "a" = append
Read: content = file.read() or for line in file: print(line)
Write: file.write("Hello World\n")
Always close: file.close() — or use the safer with statement:

Safe File Handling with open("data.txt", "r") as file: for line in file: print(line.strip()) # File closes automatically when the with block exits

Databases & SQL

What Is a Database?

An organised collection of data that can be easily accessed, managed, and updated
More powerful than a spreadsheet for large datasets: faster searching, relationships between data, multiple users
Relational database: data stored in tables (relations); tables are linked by relationships
Each row is a record; each column is a field; each table has a primary key (unique identifier for each record)

Key Database Terms

Primary key: a field that uniquely identifies each record (e.g. StudentID)
Foreign key: a field in one table that references the primary key of another table (creates a relationship between tables)
Attribute / Field: a category of information (column) — e.g. Name, DOB, Address
Record: a single row of data — all the information about one item
Query: a question asked of the database to retrieve specific data
DBMS (Database Management System): software for creating and managing databases (e.g. MySQL, SQLite, Microsoft Access)

SQL Basics

SQL (Structured Query Language) is the standard language for managing relational databases
Case insensitive, but convention is to write keywords in uppercase

Key SQL Commands SELECT name, age FROM Students WHERE age > 13; -- Retrieves name and age columns from Students table where age is over 13 SELECT * FROM Students ORDER BY name ASC; -- Retrieves all columns, sorted alphabetically by name SELECT * FROM Students WHERE name LIKE 'A%'; -- All students whose name starts with A INSERT INTO Students (name, age) VALUES ('Alice', 13); UPDATE Students SET age = 14 WHERE name = 'Alice'; DELETE FROM Students WHERE name = 'Alice';

Boolean Logic & Logic Gates

Boolean Values and Operations

Boolean: can be only True (1) or False (0)
AND: True only if BOTH inputs are True. Truth table: 0∧0=0, 0∧1=0, 1∧0=0, 1∧1=1
OR: True if AT LEAST ONE input is True. 0∨0=0, 0∨1=1, 1∨0=1, 1∨1=1
NOT: inverts the input. NOT 0 = 1; NOT 1 = 0
XOR (exclusive OR): True if inputs are DIFFERENT. 0⊕0=0, 0⊕1=1, 1⊕0=1, 1⊕1=0
NAND: NOT AND — opposite of AND. All True except when both inputs are 1.
NOR: NOT OR — opposite of OR. Only True when both inputs are 0.

Logic Gates

Logic gates are electronic circuits that implement Boolean operations
Each gate has standard symbol diagrams used in circuit drawings
AND gate: D-shaped body with flat left side
OR gate: curved body, arrow-shaped right side
NOT gate: triangle with a circle (bubble) at the output
NAND gate: AND with a bubble at the output
NOR gate: OR with a bubble at the output
XOR gate: OR gate with an extra curved line on the input side

Boolean Algebra

Simplifying Boolean expressions reduces the number of logic gates needed → cheaper circuits
Key laws: A AND 1 = A | A AND 0 = 0 | A OR 0 = A | A OR 1 = 1
NOT NOT A = A (double negation) | A AND A = A | A OR A = A
De Morgan's Laws: NOT(A AND B) = NOT A OR NOT B; NOT(A OR B) = NOT A AND NOT B
Applications: CPU design, memory addressing, search engines (Boolean search queries: "cats AND dogs", "cats NOT dogs")

Operating Systems

What Does an OS Do?

An operating system is system software that manages hardware and provides services to application software
Key functions: process management, memory management, file management, device management, user interface, security
Examples: Windows 11, macOS Sequoia, Ubuntu Linux, Android, iOS

Process Management

A process is a program that is currently being executed
The OS manages multiple processes simultaneously (multitasking) using the CPU scheduler
Process states: New → Ready → Running → Waiting → Terminated
CPU scheduling: decides which process runs next (Round Robin, Priority, First Come First Served)
Virtual memory: using part of the hard disk as if it were RAM when RAM is full — slower but prevents crashes

Memory Management

The OS allocates RAM to running processes and ensures they do not interfere with each other
Cache memory: faster than RAM, stores recently used data and instructions. L1 cache (fastest, smallest, inside CPU), L2 cache, L3 cache.
Paging: divides memory into fixed-size blocks (pages) for efficient allocation

File Systems

The OS manages how files are stored and retrieved on secondary storage
File systems: FAT32, NTFS (Windows), ext4 (Linux), APFS (macOS)
Files are organised in a hierarchical directory (folder) structure — a tree starting at the root
File permissions: read, write, execute — control who can access files
Fragmentation: files become split across non-contiguous disk sectors over time → slower access. Defragmentation reorganises files.

Cybersecurity In Depth

Social Engineering

Manipulating people into revealing confidential information rather than attacking systems directly
Phishing: fake emails from apparent trusted sources (banks, HMRC) requesting login details
Spear phishing: targeted phishing using personal information to appear genuine
Vishing: voice phishing — fake phone calls (e.g. "Your bank account has been compromised")
Smishing: SMS phishing — fake text messages with malicious links
Baiting: leaving infected USB drives in public places for curious people to pick up and plug in
Pretexting: creating a fabricated scenario to extract information (e.g. pretending to be IT support)

Malware In Depth

Virus: self-replicating code that attaches to legitimate programs; spread by human action (sharing files)
Worm: self-replicating; spreads independently across networks without human action
Trojan horse: disguises itself as legitimate software; does not self-replicate; opens a backdoor
Ransomware: encrypts victim's files; demands payment for decryption key. WannaCry (2017) affected the NHS.
Rootkit: hides its presence in the OS; gives attackers administrative access; very hard to detect
Keylogger: records every keystroke → captures passwords and private data
Adware: displays unwanted advertisements; often bundled with free software

Network Attacks

DDoS (Distributed Denial of Service): floods a server with requests from many infected machines (a botnet), making it unavailable to legitimate users
Man-in-the-middle (MITM): attacker secretly intercepts and possibly alters communications between two parties; often on unsecured public Wi-Fi
SQL injection: inserting malicious SQL code into a web form input to manipulate the database (e.g. logging in without a password, or extracting all user data)
Packet sniffing: capturing data packets as they travel across a network to steal unencrypted information
Brute force attack: systematically trying every possible password combination until one works

Protection Strategies

Encryption: data encrypted in transit (HTTPS/TLS) and at rest. Even if intercepted, data is unreadable without the key.
Firewall: monitors traffic using rules; can be hardware or software based
Intrusion Detection System (IDS): monitors for unusual network activity and alerts administrators
Two-factor / Multi-factor authentication (2FA/MFA): requires two forms of ID (password + SMS code / authenticator app / fingerprint)
Penetration testing: authorised simulated attacks by security professionals to identify weaknesses
Security policies: rules governing acceptable use, password policies, update schedules, incident response procedures
Software updates and patches: close known vulnerabilities; WannaCry exploited a Windows vulnerability for which a patch was available but many organisations hadn't applied

💻 Year 8 Computer Science