What is a machine cycle?

Question

I am a little confused about the exact definition of a "machine cycle".

For example, some sources on the Internet say this:

Four steps that the processor performs for each machine language instruction: fetch, decode, execute, and save.

While the Z80 Programming book , which supposedly has a good reputation, says:

We saw that all instructions are executed in three stages: FETCH, DECODE, EXECUTE. Now we need to introduce some definitions. Each of these phases will require several clock cycles. The Z80 executes each phase in one or more logical cycles, called a “machine cycle".

Now what confuses me is what I understood - the first one basically says: a machine cycle is a sample-decode cycle, while a book basically says: a machine cycle is one or more - a clock a cycle that occurs in each of the cycle of sampling, decoding or execution separately .

So what is this?

Answer 1

z80 has two different concepts of "cycle". The difference matters because the z80 is a multi-cycle architecture and uses both several clock cycles per step and (often) several steps for each instruction.

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