SCSI tape question

Chuck Guzis cclist at
Fri Dec 12 21:41:18 CST 2014

On 12/12/2014 07:24 PM, Jon Elson wrote:

> LOTS of SCSI devices violated the standard protocol in interesting
> ways.  My understanding is there are two classes of SCSI drives.  One
> class used a scheme that was quite like old 9-track tapes, so that
> there was essentially no formatting that wrapped around the user
> data.  So, there would be a physical gap with no magnetic transitions
>  between the written user data blocks.  There would be a CRC of some
> sort at the end of the user data.  Higher-end drives wrapped the user
> data into a more complex format, so each block would have a block
> size and a sequence number at the beginning, and maybe a trailer of
> the same info with the CRC.  Often in these systems, there would be
> NO physical gap.  This increased data capacity, but made it
> impossible to rewrite a single tape block.  The file mark was just a
> special block with minimal or zero-length data packet.

This is a bog-standard 1600 PE density 9 track tape on a 10.5" reel.
So no surprises in the physical format.  Just some screwball controller 


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