Not too bad. I was expecting the first shaving step to be about the OS media requiring 520 byte sectors and thus needing a "fancier" CD writer/reader. Maybe that was Sun, not SGI?
I think the whole 512 byte sector CD-ROM thing was common to all the 90's-era "Real UNIX" machines. They generally all wanted to treat CDs like a hard drive, for booting purposes. (PCs, on the other hand, did a different weird hack where they'd embed a floppy image at the state of the CD and the BIOS knew how to handle that.)
Yeah, you're right, they wanted 512 instead of 2048 bytes per sector to use the CD as a HD. But I think that at least one of the Unix vendors shipped the install media as 520 byte sectors, with 512 bytes of data and 8 bytes of checksum. In order to duplicate the discs, you needed to own a writer that was fancier than average (i.e. a SCSI unit, not an IDE one).
I keep a DEC RRD-40 drive (with its weird pre-caddy disc holder thing) around for the purpose of booting old DECstations. Not sure if it used 520B sectors though. I think I have the manual .. somewhere.
Yeah, I know about OS/400 using the extra bytes on hard drives for the pointer tags (not a checksum), but what I had in mind were data CDs, whose canonical sector size was 2048.