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The key word in my comment is ‘early’. You’re right about architectures today but that explicitly wasn’t what I was talking about. Caches we’re important in the

The key word in my comment is ‘early’. You’re right about architectures today but that explicitly wasn’t what I was talking about. Caches we’re important in the IBM 801 but your orher points don’t apply to early RISC designs.

sitkack 4y ago
RISC didn't hit its stride until the early 80s, using caches. The 801 was an experiment. When the 801 shipped, almost no system had hard coded microcode. Being able to update microcode in the field isn't the reason RISC thrived.
- klelatti 4y ago
  I can think of at least two of the RISC pioneers who have cited buggy CISC architectures / microcode as a key motivating reason for adopting RISC. I actually cited an example of a major CISC design that basically failed because it was so buggy. The early microprocessors all had hard coded microcode - Intel only had upgradeable microcode with P6 in the mid 1990s. I didn't say that it was the reason - there were many reasons - but that it was one factor. It was absolutely the case that original RISC designs were simpler to design and that helped them to get traction. Edit - just to add that caches enabled RISC to get decent performance but they were not by themselves a reason for choosing RISC over CISC.
- abiloe 4y ago
  > When the 801 shipped, almost no system had hard coded microcode. 1990? No system without soft microcode? That's a very restricted definition of system for the field of computing in 1990.
- skissane 4y ago
  > When the 801 shipped, almost no system had hard coded microcode. Intel 8086 was introduced in 1978, with hardcoded microcode. Intel didn’t introduce microcode patching support until the Pentium Pro in 1995.
  - sitkack 4y ago
    Intel chips were not "systems", they were disposable microprocessors. Systems have updates and field support personnel. Lousy counterfactuals sleep furiously.

sitkack 4y ago

RISC didn't hit its stride until the early 80s, using caches. The 801 was an experiment. When the 801 shipped, almost no system had hard coded microcode. Being able to update microcode in the field isn't the reason RISC thrived.

klelatti 4y ago
I can think of at least two of the RISC pioneers who have cited buggy CISC architectures / microcode as a key motivating reason for adopting RISC. I actually cited an example of a major CISC design that basically failed because it was so buggy. The early microprocessors all had hard coded microcode - Intel only had upgradeable microcode with P6 in the mid 1990s. I didn't say that it was the reason - there were many reasons - but that it was one factor. It was absolutely the case that original RISC designs were simpler to design and that helped them to get traction. Edit - just to add that caches enabled RISC to get decent performance but they were not by themselves a reason for choosing RISC over CISC.
abiloe 4y ago
> When the 801 shipped, almost no system had hard coded microcode. 1990? No system without soft microcode? That's a very restricted definition of system for the field of computing in 1990.
skissane 4y ago
> When the 801 shipped, almost no system had hard coded microcode. Intel 8086 was introduced in 1978, with hardcoded microcode. Intel didn’t introduce microcode patching support until the Pentium Pro in 1995.
- sitkack 4y ago
  Intel chips were not "systems", they were disposable microprocessors. Systems have updates and field support personnel. Lousy counterfactuals sleep furiously.