SCSI is a bus that supports both internal and external devices. To support these two
types of devices, most SCSI host adapters come with both internal and external connectors.
Internal connectors are usually mounted along the top edge of the SCSI host adapter, and
are used for the ribbon cables employed for internal SCSI devices. External connectors are
mounted along the outside edge of the host adapter (the part accessible from the back of
the PC when the card is inserted into a system bus slot.)
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Internal (above) and external (below) connectors on a
Wide Ultra2 SCSI
host adapter. In the upper photo you can see two connectors; facing you is a
68-pin (wide) high-density connector, and facing up is a 50-pin (narrow) "regular
density" connector. In the lower photo is a 68-pin (wide) high-density connector. |
The exact type of connectors provided on any given card depends on its design, and more
specifically, the type of SCSI it is intended to support. A card that is designed to
support narrow devices will have narrow (50-pin) connectors, while cards that are built to
run wide devices will have 68-pin connectors. There are also different types of each of
these two sizes of connector; for example, an older or lower-end host adapter may use the
older high-density 68-pin connectors while high-end Ultra160 card may use the smaller
very-high-density (VHDCI) connectors.
Obviously, when purchasing a host adapter check to make sure it has the connectors you
need for your devices. Remember that adapters are available to interface devices that use
different styles of connectors, but they can add significant cost to a SCSI
implementation. For much more information on cable and connector issues, see this section of the site.
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