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Question

And what will be the answer using operand forwarding ?

Answer 1

Total number of instructions = 100.

assuming stages are – IF ID EX MA WB and ID stage utilized for operand fetch. Also, ID and WB cannot overlap.
then 1^st instruction takes 5 cycles, after that each instruction adds 4 cycles.
Total cycles = 5+(99*4) = 401
then average CPI = 4.01

If ID and WB can overlap, then
Total cycles = 5+(99*3) = 302, so then average CPI = 3.02