@rygorous@mastodon.gamedev.place
Post #2409994
2025-09-09 01:59 UTC
@regehr@mastodon.social @steve@discuss.systems This is one of the bigger reasons for why ISA doesn't matter more.
Broadly, your uArch is only as good as its data movement, because that shit is what's really expensive, not the logic gates.
It's things like:
- how good is your entire memory subsystem
- how good is your bypass network
- how good are your register files
etc.
It's not like you can't make mistakes in the ISA that will really kill your design, you can. That's what happened to VAX.
Replies (1)
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@rygorous@mastodon.gamedev.place 2025-09-09 02:02
@regehr@mastodon.social @steve@discuss.systems The VAX ISA turns out to be, inadvertently, _extremely_ hostile to an implementation that tries to decouple frontend and backend, which ultimately broke its neck. x86 has many flaws, but nothing that makes it so that there is a massive discontinuity where there's basically nothing you can do about a particular problem until you have like 10x transistor/power/whatever budget, which is the kind of thing that kills archs.