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GATE CSE 2025 Session 1 Q37: Largest immediate field in a 32-bit ADD instruction

Question

A processor has 64 general-purpose registers and 50 distinct instruction types. An instruction is encoded in 32-bits. What is the maximum number of bits that can be used to store the immediate operand for the given instruction?

ADD R1, #25     // R1 = R1 + 25

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Answer: B (official GATE 2025 final answer key)

Concept used: Instruction format: opcode and register fields take fixed bits, and the rest is left for the immediate.

First step: 50 instruction types need a 6-bit opcode and 64 registers need a 6-bit register field; subtract both from 32.

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Source: official GATE 2025 Session 1 CS question paper and final answer key, organised by IIT Roorkee. Question paper · Answer key

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