Plenty of technical baggage for Xeon

Reading through Xeon Bang Per Buck, Nehalem to Broadwell, and came across this gem:

Nehalem is the touchstone against which all Xeons should be measured because this is when Intel got rid of so much technical baggage that had been holding the Xeons back.

Sure, FSB was ditched for QPI, and the memory controllers were brought on-die, but there’s still a heck of a lot of technical baggage being carried around. I started writing this in 2016. It’s now 2020. Do modern Xeons really need to continue carrying around legacy in hardware from the original 8086 and other x86 “mileposts” (80286, 80386, 80486, pentium, pentium pro, etc…)? I bet there’s a Greenlow or Denlow board somewhere in embedded land with ISA slots plumbed in through eSPI, booting DOS 6.

EFI has been shipping since 2000, and Apple started shipping Intel-based Macs with EFI in 2006. Why are we still booting in 16-bit real mode? Why did it take so long for option ROMs for modern on-board ethernet on Intel reference hardware (and PCSD’s commercial versions) to be re-coded for EFI in the intervening decade? (Whitley finally dropped real-mode opROM support.) Add a software-based 16-bit emulator for legacy option ROMs optionally loaded during DXE phase? (DEC had a MIPS emulator in turbochannel Alphas for running turbochannel option ROMs. Sun and other openfirmware systems went one better and used architecture-independent FORTH bytecode.)

The necessity for direct hardware support of legacy 32-bit support is questionable — BIOS claims it needs 32-bit to meet code-size requirements, but the code is not exactly tidy or concise. There seems to be a vicious circle between IBVs and BIOS developers unwilling to update crufty code, with long-aged code bases suffering from a tragedy of the commons, with no clear stewardship or short-term monetary payout for cleaning things up. I do have a few BIOS buddies who grok this and are trying to do what they can, but there’s a lot of momentum in technical debt that’s coming up on two decades old in a company that has historically viewed software as an enabler for hardware.

Surely 32-bit backwards compatibility could be handled at the OS and software layer, not the hardware? IA64 bungled implementation of IA32 backwards compatibility by not making it performant, but that doesn’t make it an inherently bad idea.

Don’t get me started on SMM… or maybe that’s a rant for another post.

(posted from the depths of my drafts years after it was started…)

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