Explanation:
SCSI
Type |
Transfer
speed |
bus |
SCSI-1 |
5Mbps |
8
bit bus |
Fast
Wide SCSI 2 |
20Mbps |
16
bit bus |
Ultra
Wide SCSI 3 |
40Mbps |
16
bit bus |
Ultra
2 |
40Mbps |
16
bit bus |
Ultra2
Wide |
80Mbps |
16
bit bus |
Ultra
3 |
160Mbps |
16
bit bus |
Ultra320 |
320Mbps |
16
bit bus |
Ultra640 |
640Mbps |
16
bit bus |
Device
support:
Most
older specs: SCSI ID - 0=bootable drive, 7=controller,
1-6=any other devices
SCSI
3 ultra-wide, Ultra320, Ultra640: 16 devices,
0=bootable drive, 15=controller
Internal
parallel SCSI cables have two or more 50, 68, or
80-pin connectors attached. External cables have 50 or
68-pin connectors at each end, depending on the
specific SCSI bus width supported.
The
figure below shows the connectors configuration for
80-pin SCA (Single Connect Attachment):

All of these SCSI types are parallel --
bits of data move through the bus simultaneously
rather than one at a time. The newest type of SCSI,
called Serial
Attached SCSI (SAS), uses SCSI commands but
transmits data serially. SAS uses a point-to-point
serial connection to move data at 3.0 gigabits per
second, and each SAS port can support up to 128
devices or expanders.
All
the different SCSI varieties use controllers and
cables to interface with devices
Note
that older types were given for understanding purpose
and you are unlikely to get any question on older SCSI
types, such as SCSI-1, and 2.