SCSI Adapters - SCSI Connector Adapters, HD68, HD50, CN50, DB25, VHDCI, SCA, SCA2
Using the correct scsi adapter is crucial to the ability of your scsi drives and peripherals to work properly at their maximum speed. SCSI Adapters have different types of scsi connectors and/or "genders" of connectors on each end. They are used for connecting a scsi device with one type of connector to a scsi cable or other scsi device with another type of connector. Unfortunately there have been quite a few "standard" connectors over scsi's long history. As scsi got faster and "wider", it was necessary to update the connector types to newer, "better", "faster" connector types. Since you don't want to have a seperate scsi card for each blasted type of scsi device or connector, it's far easier, and less costly to use a scsi adapter. So this is the function of the scsi adapter. Another important point when considering scsi adapters is the "wide" and "narrow" or "high byte" "low byte" problem. "Wide scsi" means 16 bit or 2 "bytes" (8 bits make a byte) scsi. Narrow scsi is 1 byte (8 bits) scsi. Connecting wide devices to a narrow bus or narroww devices to a wide bus must be done with the proper scsi adapter which takes the termination problems into account. Wide scsi devices will work just fine using only the first byte, and therefore can be used on a narrow bus (cable) as long as their connected using a scsi adapter with high byte termination. Narrow devices can be used on a wide bus, without problems depending on whether or not they are connected to an "LVD" (Ultra2/Ultra160) segment. Connecting narrow scsi devices to an LVD bus will cause that segment to drop out of LVD mode. In the case of connecting narrow external devices to a scsi controller card with an external LVD connector, it is often a good idea to use an internal/external scsi adapter to "move" an internal narrow bus to the outside of the case to connect scanners, zip drives and other external scsi peripherals.
•The basics of SCSI for newbies and technical information
•SCSI Connectivity FAQ
•SCSI Connector Pictures