COMPUTER SCIENCE AND ENGINEERING
COMPUTER ORGANIZATION
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Question
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Consider a pipelined processor with the following four stages-IF:Instruction FetchID:Instruction Decode and Operand FetchEX:ExecuteWB:Write Back The IF, ID and WB stages take one clock cycle each to complete the operation. The number of clock cycles for the EX stage depends on the instruction. The ADD and SUB instructions need 1 clock cycle and the MUL instruction need 3 clock cycles in the EX stage. Operand forwarding is used in the pipelined processor. What is the number of clock cycles taken to complete the following sequence of instructions? ADD R2, R1, R0 R2 ← R0 + R1MUL R4, R3, R2 R4 ← R3 + R2SUB R6, R5, R4 R6 ← R5 + R4
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7
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8
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9
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14
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Explanation:
Detailed explanation-1: -A pipelined processor uses a 4-stage instruction pipeline with the following stages: Instruction fetch (IF), Instruction decode (ID), Execute (EX) and Writeback (WB).
Detailed explanation-2: -A 5-stage pipelined processor has Instruction Fetch(IF), Instruction Decode(ID), Operand Fetch(OF), Perform Operation(PO)and Write Operand(WO)stages.
Detailed explanation-3: -Thus, Execution time in 4 stage pipeline = 1 clock cycle = 800 picoseconds.
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