[Solved]: Understanding Instruction Cycle?

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Problem Detail: A basic instruction cycle consists of these 5 stages.

Instruction Cycle

  1. IF – Instruction Fetch
  2. RD – Instruction Decode and Register Read
  3. EX – Execute
  4. MA – Memory Access
  5. WB – Write Back

I understood the function of all the stages accept the fourth (Memory access). What’s the significance of this stage? Over Internet what I’ve found is this

MA(Memory Access) does following operation

  • If load or store instruction, then access memory
  • If branch instruction, replace PC with destination address

The second point is clear, but I’m confused by the first. Suppose we have load and store instruction like this $$(I) R_1 leftarrow m[A_1]$$ $$(II) m[A_2] rightarrow R_2$$ what will the MA stage do for the above instructions?

Asked By : Atinesh

Answered By : 3yakuya

You have to operate on the memory to do anything useful. Reading next instruction, getting variable to operate on or saving calculated value – all that requires accessing memory.
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