SCSI : Computer Hardware Buyers’ Glossary

by Roedy Green ©1997-2008 Canadian Mind Products
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SCSI

Small Computer Systems Interface. SCSI controller cards can handle up to seven devices, usually hard disks, CD-ROMS, back up tape drives or scanners. SCSI hard disks are more expensive than the garden variety EIDE hard disks. SCSI won’t buy you any more speed if you use Windows-95. You have to use a true multi-tasking Operating System like OS/2 or NT to get the SCSI speed benefits. There are six flavours of SCSI. Home machines mostly use SCSI-2.

Types of SCSI
type	bits	pins	async MHz	sync MHz	cable meters	raw throughput Mbytes/sec
SCSI	8	50	4	5	6	5
SCSI-2	8	50	8	10	3	10
wide SCSI-2	16	68	8	10	3	20
differential SCSI-2	16	68	8	10	25	20
Fast20 aka Ultra 1	16	68	8	20	3	40
Ultra 2 SCSI	16	68	8	40	12	80
Ultra 160 SCSI	16	68	8	80	12	160

The best SCSI controllers come from Adaptec. Their website is also a good place to find technical documentation about SCSI as is Granite Digital. It is possble to mix 50-pin and 68-pin SCSI devices on the same bus using a converter, however then all devices run at the slower speed. You can also use a controller with connectors for both 50 and 68-pin cables.

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