Computer Organisation is a core part of IB Computer Science. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
CPUProcesses instructions via the fetch–decode–execute cycle.
Von Neumann architectureStores data and instructions in the same memory.
RAM & ROMRAM is volatile working memory; ROM is permanent.
CacheFast memory close to the CPU for frequently used data.
RegistersTiny, fast stores inside the CPU (e.g. the accumulator).
Clock speedHow many cycles the CPU performs per second.
Data busBidirectional bus carrying data values.
Address busUnidirectional bus carrying memory addresses.
Control busCarries timing and control signals.
FetchGet instruction from memory at PC.
DecodeCU interprets the instruction in IR.
ExecuteALU or memory performs the operation.
Memory hierarchyLayers from fastest registers to slow disk.
L1/L2/L3Cache levels increasing in size and latency.
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
What does the CPU do?✗ Permanently stores all the computer's files. ✓ Processes instructions (fetch–decode–execute).
How do RAM and storage differ?✗ They are the same thing. ✓ RAM is fast, volatile working memory; storage keeps data without power.
What does a WHILE loop do?✗ Always runs forever. ✓ Repeats while a condition stays true.
Practise Computer Organisation — free games
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