[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk Interfaces
and Configuration | Small Computer Systems Interface (SCSI) ]
Summary of SCSI Protocols and Transfer Modes
For easier comparison, the chart below shows all of the different SCSI transfer modes
and feature sets, along with their key characteristics. For your clicking pleasuer, I've
also hyperlinked everything that wasn't nailed down ;^)
Transfer
Mode |
Defining Standard |
Bus Width (bits) |
Bus Speed (MHz) |
Through- put (MB/s) |
Special
Features |
Cabling |
Signaling Method |
Maximum Devices Per
Bus |
Maximum Cable Length
(m) |
"Regular" SCSI (SCSI-1) |
SCSI-1 |
8 |
5 |
5 |
|
50-pin |
SE |
8 |
6 |
HVD |
8 |
25 |
Wide SCSI |
SCSI-2 |
16 |
5 |
10 |
|
68-pin |
SE |
16 |
6 |
HVD |
16 |
25 |
Fast SCSI |
SCSI-2 |
8 |
10 |
10 |
|
50-pin |
SE |
8 |
3 |
HVD |
8 |
25 |
Fast Wide SCSI |
SCSI-2 |
16 |
10 |
20 |
|
68-pin |
SE |
16 |
3 |
HVD |
16 |
25 |
Ultra SCSI |
SCSI-3
/ SPI |
8 |
20 |
20 |
|
50-pin |
SE |
8 |
1.5 |
4 |
3 |
HVD |
8 |
25 |
Wide Ultra SCSI |
SCSI-3
/ SPI |
16 |
20 |
40 |
|
68-pin |
SE |
8 |
1.5 |
4 |
3 |
HVD |
16 |
25 |
Ultra2 SCSI |
SCSI-3
/ SPI-2 |
8 |
40 |
40 |
|
50-pin |
LVD |
8 |
12 |
2 |
25 |
HVD |
8 |
25 |
Wide Ultra2 SCSI |
SCSI-3
/ SPI-2 |
16 |
40 |
80 |
|
68-pin |
LVD |
16 |
12 |
2 |
25 |
HVD |
16 |
25 |
Ultra3 SCSI |
SCSI-3
/ SPI-3 |
16 |
40 (DT) |
160 |
At least one of Fast-80, CRC, DV, QAS, Packet |
68-pin |
LVD |
16 |
12 |
2 |
25 |
Ultra160(/m) SCSI |
SCSI-3
/ SPI-3 |
16 |
40 (DT) |
160 |
Fast-80,
CRC, DV |
68-pin |
LVD |
16 |
12 |
2 |
25 |
Ultra160+ SCSI |
SCSI-3
/ SPI-3 |
16 |
40 (DT) |
160 |
Fast-80,
CRC, DV, QAS,
Packet |
68-pin |
LVD |
16 |
12 |
2 |
25 |
Ultra320 SCSI |
SCSI-3
/ SPI-4 |
16 |
80 (DT) |
320 |
Fast-160,
? |
68-pin |
LVD |
16 |
12 |
2 |
25 |
Some notes on this table:
- "(DT)" means that transfer mode uses double transition clocking.
- Throughput numbers are in decimal megabytes
per second.
- To keep the table from getting cluttered, I've only mentioned current cabling, not
obsolete cables.
- The number of devices includes the host adapter.
- For Ultra and faster speeds, the maximum length of cable for some signaling types
depends on the number of devices on the chain; thus, the multiple rows.
- Ultra320 specifications are not final as of this writing.
 Note: The number of
devices (8 or 16) includes the host adapter.
 Next: SCSI Host
Adapters
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