GCSE Computer Science

GCSE Computer Science hardware, without the jargon

Last updated August 2026

Hardware questions come down to three things: what the CPU does, how memory and storage differ, and what makes one system faster than another. Get those straight and the rest is vocabulary.

What the CPU is actually doing

The CPU runs the fetch-decode-execute cycle on a loop: fetch an instruction from memory, decode what it means, execute it, then fetch the next one. Inside it, the control unit manages that cycle, the arithmetic logic unit (ALU) does the maths and logic, and registers hold data the CPU needs right now — they're tiny but far faster than RAM. Von Neumann architecture is the name for storing instructions and data in the same memory, which is how most everyday computers are still built.

• Clock speed — cycles per second; higher generally means faster, measured in GHz.
• Cores — more cores can run more instructions in parallel, if the software is written to use them.
• Cache — a small block of very fast memory sitting between the CPU and RAM, storing data likely to be needed again soon.

Memory and storage, and why they're not the same thing

RAM is fast and temporary — it holds whatever's currently running and empties when the power goes off. ROM is small, permanent and holds the startup instructions a computer needs before an operating system has even loaded. Secondary storage (SSD, hard disk drive, optical disc, flash memory) is what actually keeps your files when the machine is switched off — exam questions here usually want you comparing capacity, speed, portability, durability and cost between storage types, not just naming them. Embedded systems — a washing machine's controller, a car's anti-lock brakes — use dedicated hardware built for one job only, which is why they're cheaper and more reliable than a general-purpose computer for that single task.

Questions students actually ask

What's the difference between RAM and ROM? RAM is read-write and loses its contents when powered off. ROM is read-only (or close to it) and keeps its contents permanently — it's what a computer reads first, before RAM has anything loaded into it.

Does more cores always mean faster? Only if the task can be split up and the software actually supports multiple cores — a single demanding task on unoptimised software won't speed up just because more cores exist.

Why use an SSD over a hard disk drive? SSDs have no moving parts, so they're faster to access, quieter and more durable — the trade-off is usually a higher cost per gigabyte of storage.