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When x87+MMX were added, existing programs ran unchanged. When x86-64 doubled the register sets, many existing programs ran unchanged (some features were droppe
by CalChris 5y ago
When x87+MMX were added, existing programs ran unchanged. When x86-64 doubled the register sets, many existing programs ran unchanged (some features were dropped). Compatibility was largely maintained. That compatibility was what AMD wagged in Intel's face when Intel was trying to pivot to Itanium. Intel had to then take the walk of shame and adopt AMD's approach.
Seriously, Intel took a long view towards this. x87 was a wart on the side of mole and still its unholy marriage with MMX (they shared a register set) allowed existing programs to run while creating a compatibility barrier to competitors. Competitors had to be compatible and bug compatible. The guy tasked with doing this at Transmeta almost had a nervous breakdown, not from compatibility (easy) but from bug compatibility.
IBM 360 programs still run on the Z architecture.
- woodruffw 5y agoI'm not saying it's impossible! They certainly have plenty of space in the EVEX scheme. But extending the GPRs is a much bigger lift, tooling-wise, than is adding a relatively disjoint ISA extension. Even if they can do it while preserving older encodings, it's just another speedbump at a time when Intel is probably anxious to make x86-64 as frictionless as possible. Besides, register renaming seems to be working splendidly at the uarch level. Why complicate the architectural model when the gains are already present?
- monocasa 5y ago> Even if they can do it while preserving older encodings, it's just another speedbump at a time when Intel is probably anxious to make x86-64 as frictionless as possible. Just wanted to throw out there that it was AMD that came up with x86-64's ISA rather than Intel. Intel was still pushing Itanium hard at the time.
- garaetjjte 5y agox87 instructions weren't dropped, they are still available on x86_64.
- CalChris 5y agoYeah, you're right. 64-Bit Mode Valid Thanks.
- chasil 5y agoThe original 8087 prompted the IEE-754 floating point standard, which had a profound impact on the entire field of computer science. https://news.ycombinator.com/item?id=17767925 https://news.ycombinator.com/item?id=17767925 https://news.ycombinator.com/item?id=23205225 https://news.ycombinator.com/item?id=23205225 https://news.ycombinator.com/item?id=23362673 https://news.ycombinator.com/item?id=23362673 https://news.ycombinator.com/item?id=18107165 https://news.ycombinator.com/item?id=18107165