GCSE Computer Science: Computer Systems

The computer systems paper asks you to explain how a machine works rather than to write code. It moves through the processor and the factors that make one faster than another, the difference between memory that forgets and storage that does not, the way numbers, text, images and sound are all reduced to binary, the hardware and protocols that move data between machines, and the ways a system is attacked and defended.

These ten questions are spread evenly across those five areas, two each, because a bank that drifts into one of them teaches you nothing about the others. Several ask you to calculate rather than recall — converting a binary number, working out an image file size from its dimensions and colour depth — since those are the marks most often lost to a method that is nearly right.

Exam boards set their own pseudocode and their own reference language for the programming paper, and the wording of their specifications is their copyright. Nothing here is taken from any specification, past paper or mark scheme; the questions target the subject content that every board teaches, so they are useful whichever one your school entered you for.

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• Name the registers used in the fetch-decode-execute cycle and say what each one holds
• Explain how clock speed, cache and the number of cores affect the performance of a processor
• Choose between magnetic, solid state and optical storage for a stated purpose and justify the choice
• Convert between binary and denary, and calculate an image file size from its dimensions and colour depth
• Identify the role of a switch, router, NIC or wireless access point on a network, and the purpose of common protocols
• Distinguish between forms of attack such as phishing, brute force and denial of service, and the measures that prevent each

A bitmap image is 200 pixels wide and 100 pixels high and is stored with a colour depth of 4 bits. Ignoring any metadata, what is the file size of the image in bits? — one of ten questions written for this set, alongside binary conversion, register roles, storage choice, network hardware and named attacks.