Question

Instruction set architecture of computer system has a size of 25. Each instruction has an opcode, an addressing mode field to support 9 modes and address field to access a 16 MB memory or to access one of 32 register. The system uses variable size instructions. Maximum size of instruction is x-bits and minimum size of instruction is y-bits. The value of x - y is _______

Answer 1

option (c)

Opcode = 5bits (25 instructions), mode = 4 -bits
If address field is used for memory access

Opcode

mode

address

5 4 24

$\text{Instruction size}=33-bits\Rightarrow x$

If address field is used for register access.

Opcode

mode

Reg. Reference

5 4 5

$\text{Instructions size}=14-bits\Rightarrow yx-y=33-14=19$