SCO UNIX and SCO XENIX with Archive 525MB SCSI tape units

Some problems have been experienced with Archive 525MB tape units functioning correctly in SCO UNIX and SCO Xenix systems. The problems are manifested with failure to access the tape unit correctly under Xenix and by failure to read or write 525MB tapes and/or failure to read tapes on another machine under UNIX.

The problem is caused by an incompatibility between the software tape driver and the hardware settings of the physical unit. SCO Xenix uses a 512 byte block for SCSI transfers, SCO UNIX can use 512 or 1024 byte blocks. The Archive 525MB tape streamer is now routinely jumpered to use a 1024 byte block, which is incompatible with SCO Xenix. Examination of the tape unit reveals a bank of six two pins just in front of the terminating resistor sockets.

By default the jumper is not fitted to CF0 (if fitted this enables autoload when the tape is inserted) and is fitted to CF1 (enables 1024 byte mode).

Under SCO Xenix the jumper should be moved from CF1 to CF0 to enable autoload and disable 1024 byte mode.

Under SCO UNIX V/386 3.2v4, 1024 byte mode can be used but other tape drives or SCO Xenix (and earlier SCO UNIX) systems may not be able to read the tapes. Any customer wishing to maintain compatibility across a range of tape subsystems should use 512 byte mode.

It is extremely important to note that the problems described above ONLY occur with Archive 525MB tape units fitted with Version 7 firmware. Earlier releases of firmware do not support the 1024 byte mode which is why the problem has only recently come to light. Two revisions of Archive streamer exist (as supplied by Apricot), only the current drive will routinely use version 7 firmware.

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