Fallacies and Pitfalls
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Pitfall: Implementing a complex instruction with microcode may not
be faster than a sequence using simpler instructions.
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Control is now implemented on the same chip as the processor and
cannot be changed easily (the main advantage of microprogramming).
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Caches were introduced that negated the fetch time edge for
microinstructions.
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Instruction sets are now simpler, which makes them easier to hardwire.
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CAD tools automate much of the process of implementing control.
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Fallacy: If there is space in the control store, new instructions
are free of cost.
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The space could be used, but there is still the cost of changing the
microcode and maintaining it.
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