ITPEC FE Morning October 2023 Question 11

Program counter — it holds the address of the next instruction and advances after each fetch, or is reloaded by a jump.

In the fetch cycle the CPU reads the instruction at the address in the program counter into the instruction register, then updates the program counter to point to the following instruction. A branch or jump works by writing a new address into the program counter.

Answer (d)

Why not others:

• •(a) Accumulator — holds operands and the results of arithmetic and logic operations, not instruction addresses
• •(b) Index register — holds a value added to an address to form the effective address, as when stepping through an array
• •(c) Instruction register — holds the instruction currently being decoded and executed, not the address of the next one

Key rule: The program counter says where the next instruction is; the instruction register holds the one already fetched.

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