Practice question · Put in order
Order the steps by which the CPU reads one byte out of main memory.
- The CPU stores the byte in one of its registers
- The CPU places the cell's address on the address bus
- Main memory locates the addressed cell
- The CPU asserts the read signal on the control bus
- The byte travels back to the CPU along the data bus
Hints
- Memory cannot begin anything until it knows both which cell and what operation.
- The contents can only travel once the cell has been located.
Show the answer
- The CPU places the cell's address on the address bus
- The CPU asserts the read signal on the control bus
- Main memory locates the addressed cell
- The byte travels back to the CPU along the data bus
- The CPU stores the byte in one of its registers
Why
The address must be presented before the command means anything, and both must arrive before memory can locate the cell and put its contents on the data bus. Only then does the byte reach a register. Expecting the data bus to be used first is the common error, nothing can be transferred before its address is known.
Practise Processor, Memory, and Buses
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