3.2.4 Outline the steps in the machine instruction cycle: fetch, decode,
execute and store.
Teaching Note:
A single processor model is sufficient. The study of a specific CPU
is not required.
Sample Questions:
4. Describe how the computer carries out a machine instruction. [4 marks]
JSR Notes:
The machine instruction cycle. The cycle is the cycle as seen on page 143, but I do think that it helps to include an optional step for when what is fetched is an address - which is often the case. So there are really two possibilities as the cycle cycles:
A. What is fetched is actually an address:
fetch
decode (and realize that what was fetched was an address)
fetch the data at the address which was just fetched
decode (this will now be data/instructions, rather than an address)
execute
store result
(perform next fetch)
B. When what is fetched is data or instructions
fetch
decode
execute
store result
(perform next fetch)
And for the fine details, here you go...
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