Question

A digital computer supports 2 - address and 1-address instructions. The size of instuction is 16- bits and address size is 6-bits. If these are 12 2-address instructions then minimum and maximum number of 1- address instruction supported are respectively?

• A. 0 and 256
• B. 1 and 1023
• C. 1 and 256
• D. 0 and 1024

Answer 1

The correct option is C 1 and 256

option (b)

2-address instruction


16 - ( 6 + 6) = 4-bits

Max opcode = $2^4=16$

used opcode = 12

Unused opcode = 4

16 - 6 = 10 bits

Max opcode = $4\ast 2^6=256$

Max 1-address instruction = 256

Min 1-address instructions = 1 [min 1 required to be supported]