External Connectors
No version of the standard has ever specified what kind of connector should be used. Specific types of connectors for parallel SCSI devices were developed by vendors over time. Connectors for serial SCSI devices have diversified into different families for each type of serial SCSI protocol. See the SCSI connector article for a more detailed description.
Although parallel SCSI-1 devices typically used bulky Blue Ribbon Centronics connectors, and SCSI-2 devices typically used Mini-D connectors, it is not correct to refer to these as "SCSI-1" and "SCSI-2" connectors. One valid rule is that connectors for wide SCSI buses have more pins and wires than those for narrow SCSI buses. A Centronics-50 or HD-50 connector is for narrow SCSI, while a Centronics-68 or HD-68 connector is for wide SCSI. On some early devices, wide parallel SCSI buses used two or four connectors and cables while narrow SCSI buses used only one.
The first parallel SCSI connectors were the Centronics type. They then evolved through two main stages, High-Density (HD) and most recently SCA - 80 pin.
With the HD connectors, a cable normally has male connectors while a SCSI device (e.g. host adapter, disk drive) has female. A female connector on a cable is meant to connect to another cable (for additional length or additional device connections).
Read more about this topic: Parallel SCSI
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