Installation guide

Installation
Manual No. 771971 3-15
Cable Lengths
Generally speaking, as SCSI data transfer rates increase, maximum
allowable cable lengths decrease. Transfer rates of 5 MB/sec for 8-bit SCSI
or 10 MB/sec for 16-bit SCSI will normally allow a 6 meter (20 foot)
maximum cable length on a channel. Transfer rates of 40 MB/sec for 16-bit
Ultra SCSI permit a maximum cable length of only 1.5 meters, if more than
4 devices are on the channel.
☛
Note
Strict adherence to guidelines for over-all cable length
is necessary when connecting Ultra-SCSI drives that
will operate at the higher data transfer rates of the
Fast-20 standard (refer to ANSI STD X3.131 for
information on SCSI cabling requirements).
Table 3-3. Supported SCSI Formats and Cable Lengths
* 50-pin to 68-pin adapter required
† 3 meters with up to 4 SCSI devices or 1.5 meters with more than 4 SCSI devices
SCSI Type Clock Rate Data Rate Connector Cable Length
Ultra-SCSI
(16-bit)
20 Mhz 40MB/sec 68-pin 3m (10 ft)†
Ultra-SCSI
(8-bit)
20 Mhz 20MB/sec 68-pin or
50-pin*
3m (10 ft)†
Wide SCSI-2
(16-bit)
10 Mhz
5 Mhz
20 MB/sec
10 MB/sec
68-pin 3 m (10 ft)
6 m (20 ft)
Narrow SCSI-2
(8-bit)
10 Mhz
5 Mhz
10 MB/sec
5 MB/sec
68-pin or
50-pin*
3 m (10 ft)
6 m (20 ft)
SCSI-1 (8-bit) 5 Mhz 5 MB/sec 50-pin* 6 m (20 ft)