HP/DEC/Compaq

Just going through my collection of way too many slow SCSI CD-ROM and came across a HP-labelled Toshiba that still identifies as a Toshiba. Do early HP9000 machines need special firmware bits to boot successfully off of CD-ROMS (talking HP 9000/887-G70 era and HP9000/400s), or will any CD-ROM work? The Usual Suspects seem to be silent on the issue - other than any CD-ROM will work for DOMAIN/os (which doesn't support booting off CD-ROM anyway).

There is no special firmware needed. third party cdroms will work fine. For PA-RISC this is true for all the boxes as long as they have SCSI and the necessary boot proms to boot from SCSI devices. For 68k, I'm sure 9000/400s are fine, but I wouldn't bet on all the ancient 9000/300s.
I think the same block size issue like with Suns and SGIs also applies here.

Yeah, I've only ever read of problems with CDROM booting of NeXTstep on hppa, but I expect those were due to block size issues. I've used various CDROMs with my PA-RISC systems and never had any issues with NeXTstep or HP-UX.

Ah, good - then I don't have to worry about keeping around a couple spare ancient HP drives for the 9ks.

There's plenty HP9000s that use IDE for cd/dvd too - and those will also take just about anything. But those may not suit your idea of "older" HP9000 then.

They'd suit my idea of HP-9000, but none of my machines have IDE interfaces.