14 Facts About Parallel SCSI

Parallel SCSI is the earliest of the interface implementations in the SCSI family.

The Parallel SCSI protocol defines communication from host to host, host to a peripheral device, and peripheral device to a peripheral device.

Parallel SCSI is not a single standard, but a suite of closely related standards.

All Parallel SCSI standards have been modular, defining various capabilities that manufacturers can include or not.

Parallel SCSI-2 specified a 32-bit version of Wide Parallel SCSI, which used two 16-bit cables per bus.

Parallel SCSI-2 expanded the command set with the Common Command Set for better support of devices other than disk drives, introduced command queueing and tightened up the requirements on some features that were optional in Parallel SCSI-1; parity was now mandatory and the host adapter was required to provide termination power in order to support active termination.

The maximum cable length remained 3 meters but single-ended Ultra Parallel SCSI developed an undeserved reputation for extreme sensitivity to cable length and condition .

Ultra-2 Parallel SCSI actually had a relatively short lifespan, as it was superseded by Ultra-3 Parallel SCSI.

Parallel SCSI bus goes through eight possible phases as a command is processed.

Connectors for serial Parallel SCSI devices have diversified into different families for each type of serial Parallel SCSI protocol.

On some early devices, wide parallel SCSI buses used two or four connectors and cables while narrow SCSI buses used only one.

In current practice most parallel SCSI buses are LVD and so require external, active termination.

Parallel SCSI Configured Automatically was an optional method to configure the Parallel SCSI ID without requiring user intervention for easier installation and to avoid problems.

Parallel SCSI interfaces had become impossible to find for laptop computers.