A digital computer has a memory unit with 32 bits per word. the instructions set

Question

A digital computer has a memory unit with 32 bits per word. the instructions set consist of 110 diffrent operations. all instructions has an operation code part (opcode) and two address fields: one for a memory adress and one for a register address. This particular system includes eight general purpose, user addressable registers. Registers may be loaded directly from memory, and memory can be updated directly from the registers. Direct memory- to- memory data movement operation are not supported. Each instruction stored in one word of memory.

A. how many bits are needed for the opcode?

B. how many bits are needed to specify the register?

C. how many bits are left for the memory address part of the instruction?

Explanation / Answer

a) 110 instructions implies 2^7 ( which gives 128 instructions)

7 bits are needed for opcode

b) 32-7/4 = 6 bits

c) 25-6 =19 bits

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