Computer Systems & Software

The control unit (fetches/decodes instructions and sequences operations) and the arithmetic logic unit (ALU), which performs arithmetic and logic operations.

It holds the memory address of the next instruction to be fetched and is automatically incremented (or loaded on a branch) during execution.

It holds the instruction currently being decoded and executed, after it has been fetched from memory at the address given by the PC.

Fetch the instruction, decode it, execute it (often including operand fetch/memory access), and write back the result.

It is a small storage location inside the CPU used for operands and intermediate results; it is fast because it sits on-chip with no bus or memory-access latency.

Registers, then cache (L1/L2/L3), then main memory (RAM), then secondary storage (SSD/disk), and finally tertiary/backup storage.