Systems Architecture

What Systems Architecture covers

Systems Architecture is examined in J277/01, Computer systems. It covers CPU components and the fetch-execute cycle, Factors affecting CPU performance and embedded systems.

The 3 subtopics

Each one has its own page.

• CPU components and the fetch-execute cycleThe purpose of the CPU, the fetch, decode and execute stages, the ALU, Control Unit, cache and registers, Von Neumann architecture, and what the MAR, MDR, Program Counter and Accumulator hold.Open →
• Factors affecting CPU performanceClock speed and a worked GHz figure, overclocking, how cache size and the number of cores affect performance, and why more cores or a faster clock do not always help.Open →
• Embedded systemsWhat embedded systems are and how they differ from general-purpose computers, why they are small, cheap, low-power and reliable, and examples from homes, cars, washing machines and traffic lights.Open →

What you need to know

Answer each one before you reveal it.

Take Systems Architecture further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• MAR vs MDR

  MAR: the CPU register holding the location in memory about to be read from or written to. MDR: the CPU register holding the value just read from memory or waiting to be written.

• ALU vs Control Unit

  ALU: the part of the processor that performs calculations and logical comparisons. Control Unit: the part of the processor that decodes instructions and coordinates the other components with signals.

• Program Counter vs Accumulator

  Program Counter: the register holding the address of the next instruction to fetch. Accumulator: the register holding the results of calculations done by the arithmetic logic unit.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is the purpose of the CPU?

   Model answer

   The CPU processes the instructions and data that make a computer system work. The CPU does this by repeatedly carrying out the fetch-execute cycle.

2. 2

   What happens during the fetch stage of the fetch-execute cycle?

   Model answer

   The next instruction is copied from main memory into the CPU, using the address held in the Program Counter. The Program Counter is then incremented to point to the following instruction.

3. 3

   What happens during the decode stage of the fetch-execute cycle?

   Model answer

   The Control Unit interprets the fetched instruction to work out what it means. The CU then prepares the parts of the CPU needed to carry it out.

4. 4

   What can happen during the execute stage of the fetch-execute cycle?

   Model answer

   The CPU carries out the decoded instruction. Execution may involve an ALU calculation, reading from or writing to memory, or jumping to another instruction.

5. 5

   What does the ALU do?

   Model answer

   The Arithmetic Logic Unit performs calculations such as addition and subtraction. The ALU also carries out logical operations and comparisons, such as checking whether one value is larger than another.

6. 6

   What is the role of the Control Unit?

   Model answer

   The Control Unit decodes instructions and sends control signals to coordinate the other parts of the CPU. The CU also controls the flow of data between the CPU and memory.

What is inside Levo

Six ways to work the same material.

Systems Architecture revision questions

What does Systems Architecture cover in OCR GCSE Computer Science?

3 subtopics: cpu components and the fetch-execute cycle, factors affecting cpu performance and embedded systems. Each one has its own page with questions and model answers.

How is Systems Architecture organised?

By the OCR J277 specification, subtopic by subtopic, so it matches the order you are taught it in.