IBM OPTIONS SCSI Manual Del Usuario página 168

– If more than four devices are on the SCSI device chain, the maximum
cable length cannot exceed 1.5 m (4 ft 11 in.).
– The total length of cable for a chain that comprises only Ultra2 or
Ultra160 SCSI devices must be no longer than 12 m (39 ft 4 in.).
v Older SCSI devices might not support synchronous data transfer. If you have
an older SCSI drive, CD-ROM drive, or tape drive in your computer, erratic
operation or other problems might occur during asynchronous data transfer.
If problems occur, remove the other drives on the cable, and retry the
operation. If this does not solve the problem, try using your SCSI adapter
utility to select asynchronous data transfer for use with your SCSI adapter.
v If you are attaching an Ultra SCSI device in an external enclosure and the
faster data-transfer rate does not work, use your Ultra SCSI adapter utility to
disable the faster data-transfer rate.
v Check for a jumper in the Auto Start position. When you install a jumper on
the Auto Start pins, the hard disk drive motor starts when the computer is
turned on. When the Auto Start position is open, the drive must receive a
start command from the SCSI adapter before it can startup. Some computers
expect the drive to be spinning and do not wait for a command from the
SCSI adapter. Also, you might have to select additional settings on your
SCSI adapter.
If you need more information, see the documentation that comes with your
computer and SCSI adapter.
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SCSI Hard Disk Drives for IBM PCs: User's Guide