Jonathan Gevaryahu via vcf-midatlantic writes:
AFAIK OSes which require drives with '512 byte blocks' is sort of a scsi hack. The physical data on the cd surface is 2048 byte blocks (plus ECC and subchannel data you don't normally see for 2532 bytes per sector, plus headers and sync marks etc) The whole 512 byte thing is a special mode certain cd drives have which sends each 2048 byte block to the host computer as if it was four separate 512 byte blocks/sectors, but its really just a translation layer. Not all drives do it.
The actual CD contents for these VMS cds are 2048 byte blocks, the 512 byte magic happens in the drive, AFAIK.
I could be wrong about this.
Pretty much, that's correct. However, if you want VMS to boot from the CD, it had better present the CD image in 512 byte blocks.