CertiGuide to A+ (A+ 4 Real) - Parallel SCSI Standards and Features

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CertiGuide to A+ (A+ 4 Real)
9 Chapter 10: The Small Computer System Interface, SCSI

The Three Buses

Ultra2 SCSI

Parallel SCSI Standards and Features

Table 20 summarizes the current conventional (parallel) SCSI standards and shows their most important specifications, including the bus type they usually use.

**Table 20: Current Parallel SCSI Standards**
Type	Bus Width	Maximum Clock	Burst Transfer Rate	Number of Devices	Bus Type
SCSI-1	8 bits	5 MHz	5 MB/s	8	SE
SCSI-2 Fast Narrow	8 bits	10 MHz	10 MB/s	8	SE
SCSI-2 Fast Wide	16 bits	10 MHz	20 MB/s	16	SE
SCSI-2 Dif-ferential Narrow	8 bits	10 MHz	10 MB/s	8	HVD
SCSI-2 Dif-ferential Wide	16 bits	10 MHz	20 MB/s	16	HVD
SCSI-3 Ultra Nar-row	8 bits	20 MHz	20 MB/s	8	SE
SCSI-3 Ul-tra Wide	16 bits	20 MHz	40 MB/s	16	SE
SCSI-3 Ul-tra2	16 bits	40 MHz	80 MB/s	16	LVD
SCSI-3 Ul-tra3	16 bits	40 MHz	160 MB/s	16	LVD

Table 21 show cabling specifications for various parallel SCSI standards and types.

**Table 21: Parallel SCSI Cable Lengths**
Type	Maximum Clock Rate	Maximum Bus Length	Minimum Distance Between Devices
SCSI-1	5 MHz	6 Meters	30 cm
SCSI-2 (Single Ended)	10 MHz	3 Meters	30 cm
SCSI-2 (Differential)	10 MHz	25 Meters	30 cm
SCSI-3 (Ultra)	20 MHz	1.5 Meters	30 cm
SCSI-3 Ultra2 & Ultra3 (LVD)	40 MHz	12.5 Meters	30 cm

Quick navigation to subsections and regular topics in this section

The Three Buses

Ultra2 SCSI

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