SCSI connector
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There are many different types of SCSI connectors in use in the computer industry. The long history of changes and enhancements to the SCSI standards, especially the move from parallel SCSI to serial SCSI, has led to an evolution of connectors. The following two sections describe the most common ones:
Connectors for SCSI devices and backplanes
SCSI disk-drives (and other target devices such as CDROMs) require a suitable means of connecting to the initiator. The earliest disk-drives had two or more separate connectors for SCSI signals, option signals and power. One popular type of parallel SCSI connector has always been the 50 or 68 pin header which has two rows of pins, 0.1 inches apart. This connector and its associated ribbon cable were not designed for the rigors of external use, so are often called an "internal SCSI connector." It is worth noting that they look similar to an ATA connector/cable which has 40 pins (two rows of 20).
Cost pressures have led to a simplification where all signals and power can be in the same connector. This also allows a disk-drive to be easily plugged into any position on the backplane of a SCSI enclosure. Most parallel SCSI disk-drives now include an 80-pin SCA (Single Connector Attachment) connector. This connector includes a power connection and also has long and short pins which enable hot swapping.
Serial SCSI disk-drives have recently been introduced. They include smaller connectors due to the reduced number of signals required:
- SSA disk-drives include a "unitized" composite connector.
- FC-AL disk-drives include a 40-pin SCA-2 connector.
- There is no defined iSCSI disk-drive connector.
- SAS disk-drives have an SFF 8482 connector which is form factor compatible with SATA.
Connectors for SCSI cables and enclosures
The SCSI standards also define connectors for making cables. Of course there are matching connectors for use on SCSI initiators or on enclosures that house disk-drives.
The first commonly-used SCSI cables were terminated with a Centronics-type 50-pin connector, similar to that used for early parallel PC printers. They were superseded by the smaller High-Density (HD) SCSI connector which has two variants, a 50-pin version (for 8-bit parallel busses) and a 68-pin version (for 16-bit parallel busses). You can get adapters that allow you to interconnect most types of parallel SCSI connector. An adapter from narrow to wide must include termination to work properly.
Serial SCSI busses use smaller cable connectors:
- SSA cables are terminated with 9-pin micro-D connectors.
- FC-AL cables initially used DE-9 connectors (electrical) or SC connectors (optical). More recent FC-AL cables use HSSDC connectors (electrical) or LC connectors (optical). Many FC-AL products now use an intermediate device called a GBIC (GigaBit Interface Converter) which allows more flexibility. GBICs can interconnect with a range of SFP (Small Form-factor Pluggable) connectors.
- iSCSI is interconnected using standard TCP/IP cabling, typically with RJ-45 connectors .
- SAS interconnections use either an SFF 8484 (internal connector) or an SFF 8470 (external connector, also known as an Infiniband connector).
External links
- [Pictures of parallel SCSI connectors]
- [Pictures of SSA connectors]
- [Pictures of FC-AL connectors]
- [Pictures of SAS connectors]
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