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by asveikau
1250 days ago
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> But RISC did change everything, didn't it? Iirc it's not such a meaningful distinction anymore. "CISC" x86 uses micro-operations internally. "RISC" ARM has several different instruction encodings (ARM, Thumb, Thumb-2, A64). Increasing numbers of people are working in high level languages anyway. |
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Like generations of CISC before it. That doesn't make it any less CISC.
https://userpages.umbc.edu/~vijay/mashey.on.risc.html
From that page, which collects a number of Usenet posts by John Mashey:
> The RISC characteristics:
> a) Are aimed at more performance from current compiler technology (i.e., enough registers).
> OR
> b) Are aimed at fast pipelining
> - in a virtual-memory environment
> - with the ability to still survive exceptions
> - without inextricably increasing the number of gate delays (notice that I say gate delays, NOT just how many gates).
The point b is where RISC chips really pulled away from CISC in terms of architectural design, especially chips like the MIPS, which Mashey worked on: The MIPS had a number of points where it exposed the tricks it used to pipeline more aggressively, even at the expense of making compilers somewhat harder to write and/or human assembly-language programmers think a bit harder. However, the lack of complicated addressing modes (post-increment, scale-and-offset, etc.) and the lack of register-memory opcodes with ALU operations, and total lack of memory-memory operations, is still a very common feature of RISC design.