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I am a Beginner in Computer Architecture. I don't know much about it. Why does an instruction need more than one clock cycle to execute? and why do we use Alternating Current(AC) in CPU. Is it because of the cost effective and dissipates less heat than DC or cause of something else. thanks in advance.

MITHILESH K
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    CPUs and digital logic in general run on DC power. The voltages that are varying are the clock and signals, because they have to switch to carry information. You can call that AC, but in that case the answer is "because unchanging DC voltage carries no information", so that part of the question doesn't make much sense. – Peter Cordes Sep 01 '21 at 04:43
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    Instructions don't *have* to take more than one cycle, if you build your CPU so that a cycle is long enough to run the slowest possible instruction. See [Modern Microprocessors A 90-Minute Guide!](http://www.lighterra.com/papers/modernmicroprocessors/) re: pipelining, although you might need a starting point of even simpler concepts like a microcoded or otherwise multi-cycle CPU that takes a variable number of cycles for simple / complex instructions. – Peter Cordes Sep 01 '21 at 04:43
  • Wooah cool. Thanks a lot – MITHILESH K Sep 01 '21 at 11:31
  • You can also take a look at J1 CPU - both single-cycle and fast at the same time, thanks to a smart ISA encoding. – SK-logic Sep 01 '21 at 13:40
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    @PeterCordes After reading the 90-minute guide I'm a new man. It has been revolutionary for my brain what I have learn there. – ABu Aug 12 '23 at 14:22

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