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Reply to @krono@toot.berlin
David Chisnall (*Now with 50% more sarcasm!*)@david_chisnall@infosec.exchange (2026-08-24 21:38:21)
@krono @whitequark
SPARC had an open ISA. Leon was a series of 32-bit SPARC backed by ESA. Sun also opened the UltraSPARC T1. Both were fairly low-end cores (the T1 was okay in aggregate but pretty slow per core).
SPARC had a bunch of interesting ideas. Register windows are one of those ideas that was good on simple cores, annoying on more complex ones, but I think would actually be nice on a very high-end core if you nicely integrate it with register rename and asynchronous spill, but not quite the way SPARC specifies it. SPARC had a simple SIMD extension, but it was roughly comparable to MMX, nothing newer.
SPARC at Sun / Oracle stagnated because the Rock team (building high-per-thread performance cores) and the Niagara team (building massively multithreaded systems) hated each other. To add anything new to the architecture required both to agree, but if one agreed the other would disagree on principle. So the architecture is quite a nice '90s design that hasn't evolved.
After the Oracle acquisition, everyone got quite nervous that Oracle probably had some patents on things that might be necessary for good SPARC implementations and would be very aggressive about enforcing them.
POWER is more fun. When I was at Microsoft, we had a choice for first-party cores for Azure (later cancelled in favour of first-party SoCs using Arm-licensed cores) of:
Buy AMD and do x86. AMD's market cap was $30 B, so easily affordable (Microsofts' was around $850 B), but probably impossible to get past the regulators. They were already tested at-scale in Azure and Xbox, not clear what would be useful differentiation.
An in-house ISA. We went a really long way along this and concluded that we could do 0-20% (depending on workload) better performance than AArch64 by learning from their experience. The cost of this would be huge for the software ecosystem and most customers weren't willing to pay for performance so the business case wasn't there.
AArch64 is a nice matur
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Michael Engel@me_@sueden.social (2026-08-24 23:33:39)
@david_chisnall @krono @whitequark The OpenSPARC T2 is also available from Oracle, but I can’t recall the differences to the T1: https://www.oracle.com/servers/technologies/opensparc-t2-page.html
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David Chisnall (*Now with 50% more sarcasm!*)@david_chisnall@infosec.exchange (2026-08-24 23:52:54)
@me_ @krono @whitequark
As I recall, the main difference was more FPU pipelines (one per core rather than a shared one?). It looked like a fairly minor tweak.