Question

A system has 32-bit architecture with 1-word long instruction. The system supports 25 distinct instructions. maximum of 16-addressing modes and maximum of 1 MB byte addressable main memory. Each instruction has 4 fields, namely, one opcode. one addressing mode field, one register reference field and one memory address field. Maximum no. of CPU registers possible in such system is ______________

• A. 7
• B. 9
• C. 8
• D. 10

Answer 1

The correct option is C 8

option (b)

Architecture = 32-bits. mean I word = 32-bits
$\text{No. of distinct instructions supported}=25\Rightarrow opcode=5–bits$
$\text{No. of addressing modes}=16\Rightarrow \text{mode field}=4-bits$
$\text{Memory size}=1MB\Rightarrow \text{memory address}=20-bits(2^{20}=1M)$
Instruction format:-


register reference = 32 -(5 +4 +20) = 3-bits

$\text{maximum No. of registers possible}=2^3=8$