[vcf-midatlantic] Found: VMS Hobbyist CDs

VAXman at tmesis.org VAXman at tmesis.org
Tue Jun 6 15:49:11 EDT 2017

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.

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