Rick Stevens wrote:
Well, way back when, Sun used a 512-byte sector size on CDs, too (Sun SPARC SLC, etc.). I never did figure out why.
It was a hack to be able to boot from CD-ROM.
Old SPARC boot code can boot only from disks that have 512-byte sector size. When CD-ROMs become popular, the only way to boot SPARC machine off CD-ROM was to use 512-byte sector size. Since back than you couldn't simply flash new version as you would do on newer machines, you were stuck with version you got on the motherboard. I don't know if SPARC machines were the only ones with that problem, but almost all SCSI CD-ROM drives from that era have jumper that controls the sector size upon power-on (name for the jumper is not standardized, and sometimes is confusing, "block" is often used, and I saw some drives that had it, but it was not mentioned anywhere in documentation).
Once the OS is up and running, it can use either 512 or 2048-bytes sectors. So you need that "special" CD-ROM drive only if you want to boot from CD-ROM media on an very old SPARC machine.
Basically all Ultra machines, and probably SS5/10/20 (not sure for all of them) can boot from any CD-ROM drive. Anything older, and you probably need 512-bytes per sector capable drive.
Also, on most CD-ROM drives from that time you can swtich from 512 to 2048 and back using more or less standard SCSI commands. Later versions of boot PROM can also boot from both 512 and 2048 bytes per sector media.
-- Aleksandar Milivojevic <amilivojevic@xxxxxx> Pollard Banknote Limited Systems Administrator 1499 Buffalo Place Tel: (204) 474-2323 ext 276 Winnipeg, MB R3T 1L7
