The role of memory in computation

The following steps outline the way in which memory interacts with the processor during computational cycles, once the bootstrapping process has completed and the OS kernel is itself loaded into memory.

1. A file is loaded from the harddisk into memory.
2. The instruction at the first address is sent to the CPU, travelling accross the data bus part of the system bus.
3. The CPU processes this instruction and then sends a request accross the address bus part of the system bus for the next instruction to the memory controller within the chipset.
4. The chipset finds where this instruction is stored within the DRAM and issues a request to have it read out and send to the CPU over the data bus.

This is a simplified account; it is not the case that only single requests are passed back and forth. This would be inefficient and time-wasting. The kernel sends to the CPU not just the first instruction in the requested file but also a number of instructions that immediately follow it.

Every part of the above process - the journey accross the bus, the lookup in the controller, the operations on the DRAM, the journey back accross the bus - takes multiple CPU clock cycles.