SCSI-3 This standard is referred to as SCSI today. It includes the SCSI
Parallel Interface (SPI), which defines the 68-pin high-density connection or
SCSI-3 connector. SPI-2 and SPI-3 have improved the connection to include
the SCA and the very high-density connectors and speeds up to 160MBps.SCSI Voltage Differentials
There are three types of signaling used on a SCSI network: Single-ended (SE) SCSI This type of signaling is used in Fast and Ultra SCSI
and allows devices to attach to a terminated SCSI bus chain with a total length
of not more than three to six meters.
High-voltage Differential (HVD) SCSI This signaling technology allows
the SCSI chain to spread out a bit more by lengthening the total bus length to
25 meters.
Low-voltage Differential (LVD) SCSI This less-costly signaling technology
builds the data transceivers into the device controllers. The overall distance of
the SCSI bus is reduced to 12 meters, however.(^506) PC Hardware: A Beginner’s Guide
Figure 19-19. Internal SCSI connectors