Computer Science GCSE

CPU (Central Processing Unit)

The hardware component that processes data and instructions.

Main Parts of the CPU

• ALU (Arithmetic Logic Unit): Performs calculations and logic operations.

• Control Unit: Manages data flow and instructions.

• Registers: Miniature, high-speed memory modules within the CPU.

CPU Registers Functions

• CPU : Stores the address of the next instruction.

• MAR : Stores the address being currently accessed.

• MDR : Stores the data being transferred.

• CIR: Stores the current instruction being executed.

The Fetch–Decode–Execute Cycle

1. Fetch: Retrieve instruction from memory

2. Decode: Interpret the instruction

3. Execute: Carry out the instruction

CPU Performance Factors

• Clock speed: The number of cycles executed per second.

• Cores: Allows more tasks to be processed simultaneously.

• Cache: Very fast memory storing frequently used data (reduces access time compared to RAM).

RAM vs ROM

• RAM (Random Access Memory): Volatile, temporary storage for running programs and data.

• ROM (Read Only Memory): Non-volatile storage for boot-up instructions.

Types of Secondary Storage

• Magnetic: HDD (cheap, high capacity, slow).

• Solid-state: SSD or USB (fast, durable, expensive).

• Optical: CD or DVD (portable, slow).

Embedded Systems

A computer system built into a larger device with one dedicated function.

• Characteristics: Single purpose, low power, high reliability.

• Examples: Washing machines, traffic lights, microwaves.

Image Data: Resolution and Colour Depth

• Resolution: The total number of pixels in an image.

• Colour depth: The number of bits used per pixel.

• Impact: Increasing either leads to a larger file size.

Types of Compression

• Lossy: Permanently removes data to create smaller files (e.g., JPEG, MP3).

• Lossless: No data is lost, though files are larger than lossy ones (e.g., ZIP).

Pillars of Computational Thinking

• Decomposition: Breaking a problem down into smaller parts.

• Abstraction: Removing unnecessary details to focus on important parts.

• Algorithm: A precise, step-by-step solution to a problem.

Searching Algorithms

• Linear search: Checks every item in a list sequentially.

• Binary search: Splits a sorted list in half repeatedly (must be sorted first).

Sorting Algorithms

• Bubble sort: Compares and swaps adjacent values.

• Merge sort: Splits the list into individual items and then merges them back in order (faster for large lists).

• Insertion sort: Builds a sorted array one element at a time by repeatedly taking the next unsorted element and inserting it into its correct position within the already-sorted portion.

Programming Basics (Python)

• Sequence: Instructions executed in specific order.

• Selection: Decisions using if, elif, and else.

• Iteration: Repeating tasks using for or while loops.

• Syntax: Uses indentation and colons (:).

Python Data Types

• Integer: Whole numbers.

• Float: Decimal numbers.

• Boolean: True or False values.

• String: Text strings.

Boolean Logic Gates

• AND: Output is true only if both inputs are true.

• OR: Output is true