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Can ALU run different instructions at the same time?


@locked. This is a good review question. Who can help us with the answer?


@kayvonf @locked No, since only one instruction at a time is fetched for all ALUs to execute. As a result of this, we saw in slides 33-36 that in cases of conditional execution, sometimes the output of some ALUs is ignored because the instruction that was fetched only applies to the data going through some but not all of the ALUs.


One of the drawbacks of using SIMD instructions is that we have to wait for all of the ALU's to finish executing the instruction before we can move onto executing another instruction.