A+ Certification SCSI Information

Interface	Connector	Clock	Maximum
Interface	Connector	Clock	Throughput	Length (single ended)	Length LVD	Length HVD	Devices
SCSI-1	IDC50; Centronics C50	5 MHz (8-bits)	5 MB/s	6 m	NA	25m	8
Fast SCSI (SCSI-2)	IDC50; Centronics C50	10 MHz (8-bits)	10 MB/s	1.5-3 m	NA	25m	8
Fast-Wide SCSI (SCSI-2; SCSI-3 SPI)	2 x 50-pin (SCSI-2); 1 x 68-pin (SCSI-3)	10 MHz (16-bits)	20 MB/s	1.5-3 m	NA	25m	16
Ultra SCSI (SCSI-3 SPI)	IDC50	20 MHz (8-bits)	20 MB/s	1.5-3 m	NA	25m	8
Ultra Wide SCSI (SCSI-3 SPI)	68-pin	20 MHz (16-bits)	40 MB/s	1.5-3 m	NA	25m	16
Ultra2 SCSI (SCSI-3 SPI)	50-pin	40 MHz (8-bits)	40 MB/s	NA	12m	25m	8
Ultra2 Wide SCSI (SCSI-3 SPI)	68-pin; 80-pin (SCA/SCA-2)	40 MHz (16-bits)	80 MB/s	NA	12m	25m	16
Ultra3 SCSI (SCSI-3 SPI)	68-pin; 80-pin (SCA/SCA-2)	40 MHz DDR (16-bits)	160 MB/s	NA	12m	NA	16
Ultra-320 SCSI	68-pin; 80-pin (SCA/SCA-2)	80 MHz DDR (16-bits)	320 MB/s	NA	12m	NA	16
Ultra-640 SCSI	68-pin; 80-pin	160 MHz DDR (16-bits)	640 MB/s				16

Table 1: Parallel SCSI Versions, retrieved from http://en.wikipedia.org/wiki/SCSI

Figure 9: External SCSI Connectors

SCSI comes with a variety of connectors, both internal and external. The table above describes some of the connectors based on which version of SCSI you are using.

Figure 10: Internal SCSI Cable

One of the primary differences between SCSI and ATA adapters is the number of devices one port supports. SCSI supports either 8 or 16 devices, depending on the version you are using, with the SCSI adapter card being one device. Each device has a unique SCSI ID in the chain, from 0-7 or 0-15. The SCSI host adapter is typically SCSI ID 7 – the ID with the highest priority on a narrow (8 device) or wide (16 device) host adapter.

Figure 11: HD68 LVD SCSI Terminator

The other difference between SCSI and other types of drive connections is that the SCSI “chain” of devices has to be terminated on each end. A terminator tells the SCSI host adapter that it’s connection is the last in the chain of SCSI connections. Typical SCSI host adapter cards (or integrated SCSI ports on motherboards) have a built-in terminator. If you are using external SCSI devices, a lot still use a terminator device which plugs into one of the SCSI ports on the device to signal it is the last device in the SCSI chain.

A+ Certification SCSI Information

A+ Certification SCSI Information (Continued)

by Jeremy Reis on Tuesday, January 22, 2008