Are old SCSI tape drives not all created equal?

[Maciej W. Rozycki]

On Wed, 17 Aug 2016, Mouse wrote:

> SCSI is more than just the physical interface.  Traditional SCSI is a
> parallel interface, with a bunch of signals and grounds.  But, layered
> atop the physical interface, there is also a command/response protocol
> which is, strictly, independent of the physical layer.  (I have seen it
> said that the SCSI protocol is very similar to both ATAPI and SAS,
> probably because it influenced their design, though I haven't read
> enough of any of them to really have a good handle on it myself.)

 I don't know of SAS offhand, however ATAPI is pretty much SCSI over ATA.  
That is really SCSI commands and responses wrapped into the so called ATA 
packets (hence the ATAPI acronym, standing for ATA Packet Interface) which 
are chunks of data sent and retrieved with the ATA data write and read 
commands.  The USB storage protocol works similarly as well.

 FWIW,

  Maciej