computer science - computer systems

aqa Computer Science

What is a computer system?

A system that takes inputs, processes data, and produces outputs using hardware and software.

What is the difference between hardware and software?

• Hardware – The physical parts of a computer (e.g., CPU, RAM, SSD).

• Software – Programs that run on a computer (e.g., OS, applications).

What is a computer system?

A system that takes inputs, processes data, and produces outputs using hardware and software.

What is the difference between hardware and software?

• Hardware – The physical parts of a computer (e.g., CPU, RAM, SSD).

• Software – Programs that run on a computer (e.g., OS, applications).

What are the two main types of software?

1. System Software – Controls the computer (e.g., OS, drivers, utilities).

2. Application Software – Used by users for tasks (e.g., Word, Photoshop).

What is an Operating System (OS)?
A: Software that manages hardware and so

Software that manages hardware and software, providing an interface for users and applications.

Name four key functions of an Operating System.

1. Memory management – Allocates RAM to programs.

2. Process management – Runs multiple applications at once.

3. File management – Organizes and stores files.

4. Device management – Controls hardware like printers and keyboards.

What are the two main types of user interfaces?

• CLI (Command-Line Interface) – Text-based, used by advanced users (e.g., Linux terminal).

• GUI (Graphical User Interface) – Uses icons, windows, and menus (e.g., Windows, macOS).

compare CLI vs GUI

CLI is faster, but GUI is easier to use.

What is the difference between memory and storage?

• Memory (RAM & Cache) – Temporary, fast, used while programs run.

• Storage (SSD, HDD) – Permanent, stores files and OS.

What’s the difference between RAM and ROM?

• RAM (Random Access Memory) – Volatile, stores temporary data.

• ROM (Read-Only Memory) – Non-volatile, stores BIOS/Firmware.

compare RAM vs ROM

RAM is faster than storage but loses data when powered off.

What is virtual memory?

A section of the hard drive used as extra RAM when RAM is full.

Name three types of secondary storage.

• HDD (Hard Disk Drive) – Cheap, slow, mechanical.

• SSD (Solid-State Drive) – Fast, expensive, no moving parts.

• Optical (CD/DVD) – Used for backups, slow.

What is cloud storage?

Data stored on remote servers, accessed via the internet (e.g., Google Drive).

pros and cons of cloud storage

Pros: Access from anywhere, no hardware needed.
Cons: Requires internet, security risks.

What is the CPU (Central Processing Unit)?

The "brain" of the computer that processes instructions.

Measured in GHz (speed) and has multiple cores for multitasking.

What are CPU registers?

Small, fast storage locations inside the CPU used for quick data access.

examples - Accumulator, Program Counter, MAR, MDR

What are the three stages of the CPU cycle

• Fetch – Gets instruction from RAM.

• Decode – Understands the instruction.

• Execute – Runs the instruction.

Name three factors that affect CPU performance.

• Clock speed – Higher GHz = faster.

• Number of cores – More cores = better multitasking.

• Cache size – More cache = faster access to frequently used data.

What is a virtual machine (VM)?

Software that simulates a computer inside another computer.

Used for testing software, running different OS, or cybersecurity.

What is emulation?

Software that imitates different hardware (e.g., playing PlayStation games on a PC).

Used in gaming, legacy software, and software testing.

What’s the difference between open-source and proprietary software?

• Open-source – Free, can be modified (e.g., Linux).

• Proprietary – Paid, owned by a company (e.g., Windows, Photoshop)

What is utility software?

Small programs that help maintain a computer system (e.g., antivirus, backup software).

What does compression software do?

Reduces file sizes to save space (e.g., ZIP, RAR).

What is defragmentation?

Reorganizing files on a hard drive to improve speed.

Not needed for SSDs (they don’t fragment).

What are the two types of backup?

1. Full backup – Copies everything, takes time.

2. Incremental backup – Only new/changed files, faster.