GATE CS 2018 Set 1 — Question 61
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Computer Organization & Architecture → Instructions & Addressing Modes → Instruction Formats
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Question
A processor has 16 integer registers (R0, R1, .. , R15) and 64 floating point registers (F0, F1,… , F63). It uses a 2-byte instruction format. There are four categories of instructions: Type-1, Type-2, Type-3, and Type-4. Type-1 category consists of four instructions, each with 3 integer register operands (3Rs). Type-2 category consists of eight instructions, each with 2 floating point register operands (2Fs). Type-3 category consists of fourteen instructions, each with one integer register operand and one floating point register operand (1R+1F). Type-4 category consists of instructions, each with a floating point register operand (1F). The maximum value of is __________.
Correct answer
32 to 32
Solution
To find the maximum value of , we calculate the total number of instruction combinations possible in a 2-byte (16-bit) format and subtract the combinations used by Type-1, Type-2, and Type-3 instructions.
Remaining = .
Each Type-4 instruction uses combinations.
.Thus, the maximum value of is 32.
1.Total combinations available: .
2.Register addressing bits:
- Integer registers (16): bits per register.
- Floating point registers (64): bits per register.
- Type-1: 4 instructions with 3 integer registers (3Rs).
- Type-2: 8 instructions with 2 floating point registers (2Fs).
- Type-3: 14 instructions with 1 integer and 1 floating point register (1R+1F).
4.Remaining combinations for Type-4:
Total used = .Remaining = .
5.Calculate :
Type-4 instructions have 1 floating point register (1F), which uses 6 bits.Each Type-4 instruction uses combinations.
.Thus, the maximum value of is 32.
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