what is difference between instruction access and data access

问题

I only learned the equation

1. all access = instruction access + data access
2. read = instruction access + load
3. write = instruction access + store

I think that I'm not fully understand the difference between 'instruction access' and 'data access' The most curious thing is that why 'read' include 'instrution access'. Could anybody explain this??? :'-(

回答1:

The processor must know what to do before doing it. So, instruction access is like knowing what operation to do and knowing the source and destination operands while data access is actually fetching the data and performing the required operation.

Here, read means that you have to read some data, but the processor needs to know that the operation is read. Also, it needs to know the source of read. To know this information it takes one instruction access. Then the processor performs the actual read which takes one data access. Same is applicable for writes.

来源：https://stackoverflow.com/questions/32800552/what-is-difference-between-instruction-access-and-data-access