Question

A digital computer has a memory unit with 32-bits per word. The instruction set architecture size is a 250. All instructions supported by computer have one mode field to support 10 addressing modes and an address field: apart from opcode field. The maximum allowable size of memory (in MB) if each instruction is stored in one word is__________.

Answer 1

option (a)

$\text{No. of instructions = 250}\text{opcode bits}=\lceil {\log }_{2}250\rceil =8-bits\text{No. of modes = 10}\text{Mode-bits}=\lceil {\log }_{2}10\rceil =4-bits\text{Instruction}$

$\text{Address bits}=32-(8+4)=20-bits\text{Memory size}=2^{20}\ast 32-bits=2^{20}\ast 4-B=4MB$