For a quick overview of SCSI, we have provided this table (courtesy of Boot Magazine):
Don't let the table intimidate you. It shows the overall history of SCSI devices, but doesn't have that much effect on buying them, because SCSI devices are backward compatible.
Terms |
Bus Speed (MB/sec) |
Bus Width (Bits) |
Max Cable Length (Meters) |
SE 2 |
HVD 3 |
LVD 4 |
|
Devices supported |
SCSI-1 |
5 |
8 |
6 |
25 |
- |
8 |
SCSI-2 |
10 |
8 |
6 |
25 |
- |
8 |
|
|
|
|
|
|
|
SCSI-3 |
20 |
8 |
1.5 |
25 |
- |
16 |
SCSI-3 |
20 |
8 |
3 |
- |
- |
4 |
SCSI-3 1 |
20 |
16 |
6 |
25 |
- |
16 |
|
|
|
|
|
|
|
SCSI-3 UW |
40 |
16 |
- |
25 |
- |
16 |
SCSI-3 UW |
40 |
16 |
1.5 |
- |
- |
8 |
SCSI-3 UW |
40 |
16 |
3 |
- |
- |
4 |
|
|
|
|
|
|
|
SCSI-3 U2 |
40 |
8 |
- |
12 |
12 |
8 |
SCSI-3 U2 |
80 |
16 |
- |
25 |
25 |
2 |
SCSI-3 U2W |
80 |
16 |
- |
12 |
12 |
16 |
SCSI-3 U2W |
80 |
16 |
- |
25 |
25 |
2 |
|
|
|
|
|
|
|
SCSI-3 U3 |
160 |
16 |
- |
12 |
12 |
16 |
1 Fast Wide SCSI 2 Single End Transceiver 3 High-Voltage Differential 4 Low-Voltage Differential
The number of devices includes the card, so for total number of peripherals, subtract 1 to get the number of devices you can add to your system.
There are a number of advantages to SCSI. First, every SCSI device has its own processor chip that allows it to do some actions without direct access to the CPU at the time. This means that SCSI devices are able to multi-task, meaning perform different tasks simultaneously, and that SCSI devices provide a lower CPU load. For servers, or high-end workstations, SCSI is the bus of choice for these very reasons, and because it can handle so many devices using 1 IRQ. For example, try to set-up a server with 15 hard drives using the IDE interface. It isn't easy!! With SCSI, it is a simple enough process.
That multitasking ability and the speed of the bus also make the SCSI interface the bus of choice for high-end scanners and for CD burners. SCSI scanners are generally faster and can handle more data then other interfaces, and SCSI CD-ROMs and CD burners are able to handle direct duplication with less chance of buffer overruns.
In addition, the fastest hard drives in the world use the SCSI interface. Best
known are the Seagate Cheetahs, but IBM also offers SCSI drives at 10,000 rpm.
Page 1: This page, introduction to SCSI
Page 2: Choosing SCSI devices
Page 3: Setting up a SCSI chain
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