ITPEC FE Subject A April 2026 Question 9

Instruction register — a fetched instruction is held there while the instruction decoder interprets it.

In the fetch cycle the program counter supplies the address, the instruction at that address is read from main memory into the instruction register, and the decoder decodes the contents of that register. Box a sits exactly between main memory and the decoder.

Answer (c)

Why not others:

• •(a) Accumulator — holds operands and arithmetic results, not the instruction being decoded
• •(b) Data cache — holds data, not instructions; fetched instructions go through an instruction cache, and in any case a cache feeds a register, not the decoder directly
• •(d) Program register (program counter) — holds the address of the next instruction, not the instruction itself

Key rule: The program counter holds an address, the instruction register holds the instruction, and the accumulator holds data being computed.

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