Recall from Chapter 9 that memory systems use the fetch-store paradigm in which
a processor can either fetch (i.e., read) a value from memory, or store (i.e., write) a
value to memory. A bus uses the same basic paradigm. That is, a bus only supports
fetch and store operations. As unlikely as it seems, we will learn that when a processor
communicates with a device or transfers data across a bus, the communication always
uses fetch or store operations.
The point is:
Like a memory system, a bus employs the fetch-store paradigm; all
control or data transfer operations are performed as either a fetch or
a store.