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by temac
2021 days ago
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CISC and RISC are mostly an ISA concept. Most chips are "microcoded", at least here and there. The term does not define a whole micro-architecture, esp in modern complex ones, but I'm not really sure how you would implement old school CISC chips without microcode concepts. The 8086 was microcoded: https://www.reenigne.org/blog/8086-microcode-disassembled/. It basically means that "you" program some low level internal details of a chip, e.g. the muxes connecting various buses to execution units. Most of the time the "you" is only the chip designers, and it is stored mostly in a ROM. Sometimes microcoding is accessible by actual software programmers, but it is quite rare. And modern u-ops are not necessarily like what was done at the time of old-school microcode. |
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