A DAT tape written on one model of a SCSI DAT drive cannot be read
          on a different model of SCSI DAT tape drive.

          SCSI DAT tape drives are often not interchangeable when read on
          a different make/model of drive than the tape was written on.
          There are two reasons for this:

          Blocking Factor
          ===============

          DAT tape drives use either a variable or fixed block size.  Each
          drive has a default blocking factor that is determined by the
          drive's hardware/firmware.  It is not related to the blocking
          factor used by tar or cpio.  Presently, the SCO tape drivers
          use the drive's default block size.  There is no way to change
          this block size in the software.

          For example, an Archive DAT tape drive uses the blocking factor
          of 1k bytes per block.  The Hewlett-Packard DAT uses the blocking
          factor of 2k bytes per block.   A Hewlett-Packard DAT cannot read
          a tape written on an Archive DAT.


          Data Compression
          ================

          Data compression is performed at the firmware/hardware level.
          Some Hewlett-Packard DAT drives and the Compaq DAT drives do data
          compression.  There is no standard for data compression and the
          tape drive manufacturers use different data compression formats.
          Thus, it is unlikely for two models of DAT drives that use data
          compression to be able to read each other's tapes.