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I recently learned about how microcode works from this video actually https://youtu.be/Zg1NdPKoosU https://youtu.be/Zg1NdPKoosU. It might not be the state of th

• gmueckl 7y ago
  My personal "Aha!" moment about this was in front of an old Zuse Z5 in a museum with a block diagram of the CPU hanging next to it. That diagram showed which bits toggled which functional unit within the CPU. The comtrol panel on the operator desk had the same bit labels on the data input buttons. This early machine had no modern instruction decoder at all. Each bit in an instruction word was used directly. This becomes wasteful when the number of functional units grows and not all bit combinations are reasonable. So the next reasonable thing to do is to introduce a lookup table from shorter coded instructions to the actual control bit patterns. The CPU in this video adds an internal step counter that allows splitting an instruction over multiple cycles with a different control word for each cycle. Modern CPUs are probably conceptually similar, but much more complex. Optimizations like pipelining and multiple ALUs make the whole decoding and checking process more complex and more dynamic.