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4.4 SCSI Cables. The most important ingredient in the successful installation of any
SCSI system is proper cabling. Many round SCSI cables are, at best, marginal on
single-ended systems and will not work at all on differential SCSI systems.
Many other round SCSI cables are assembled in a manner that has no regard for
wire pair selection. These cables appear to work most of the time but may cause
intermittent problems on the SCSI bus that are extremely difficult to
troubleshoot. Also, the longer the SCSI cables, and faster the maximum bus
speed, the more important a factor the cables become. Because of these “cable
factors”, should you have problems getting your system to work properly with
Paralan iS5xx series Bridges, we suggest temporarily replacing your round SCSI
cables with flat twisted pair ribbon cables as they are normally SCSI correct.
Also, contact Paralan for our “SCSI Quiet Cable” data sheet. Note, the maximum
number of devices allowed on the SCSI bus and the maximum bus cable length
are determined by the bus speed and bus width of the system (see Table 1 below).
Table 1
Bus Speed, Bus Max.*
STA Terms ANSI Terms
MBytes/Sec. Width, Max. Bus Lengths, Meters Device
Max. bits Single- ended LVD HVD Support
SCSI-1 (narrow)
FAST-5
5 8 6 25 25 8
Fast SCSI (narrow)
FAST-10
10 8 3 25 25 8
Fast Wide SCSI
FAST-10
20 16 3 25 25 16
Ultra SCSI (narrow) FAST-20 20 8
1.5
3
25
25
25
25
8
4
Wide Ultra SCSI FAST-20 40 16
N/A
1.5
3
25
25
25
25
25
25
16
8
4
Ultra2 SCSI (narrow)
FAST-40 40 8 N/A
25
P
12
M
N/A
N/A
8
Wide Ultra2 SCSI FAST-40 80 16 N/A
25
P
12
M
N/A
N/A
16
Ultra3 SCSI or
Ultra160 SCSI
FAST-80 160 16 N/A
25
P
12
M
N/A 16
Ultra320 SCSI FAST-160 320 16 N/A
25
P
12
M
N/A 16
P = Point-to-point interconnect. Only 1 SCSI Initiator and 1 Target on the bus.
M = Multidrop interconnect. At least 1 SCSI Initiator and 2 Targets on the bus.
* = Includes all SCSI Targets and Initiators.