AQA 8525 3.4.5: Systems architecture
The free BugBot lessons that teach this point, a robot to try it on, and the past-paper questions that test it.
What it covers
The CPU, the central processing unit, is the part of a computer that runs programs. BugBot's is the processor on its top board, and it carries out millions of instructions every second. Each one goes through the same three steps, over and over: fetch an instruction from memory, decode it, and execute it. This lesson opens the CPU up and runs the cycle by hand.
- Inside the CPU
- Buses
- The fetch-decode-execute cycle
- Instructions are numbers too
Or do it in the simulator, with tasks that mark themselves
Lessons that teach it
- F9.4 The CPU and fetch-execute Logic and computer systems
The ALU, control unit, registers and buses, and tracing the fetch-decode-execute cycle. - F9.5 CPU performance Logic and computer systems
Clock speed, cores and cache, measured with models. - F9.6 Memory Logic and computer systems
RAM, ROM, cache and virtual memory. - F9.7 Secondary storage Logic and computer systems
Magnetic, optical, solid state and cloud storage, and choosing between them. - F9.8 Embedded systems: inside BugBot Logic and computer systems
What makes a system embedded, the robot's three boards, and the sense-decide-act loop.
Try it on a robot
The task from F9.4 The CPU and fetch-execute, running here. Change the program and press Run.
The specification is AQA's own document; this page says which of our lessons teach point 3.4.5 and is not endorsed by the board.