This is a quick reference table for SCSI transfer rates for my own reference. It is blatantly stolen from Wikipedia.

Interface Connectors Width Bandwidth Devices
Narrow SCSI IDC50, C50 8 bits 5MB/s 8
Fast SCSI IDC50, C50 8 bits 10MB/s 8
Fast/Wide SCSI HD68 16 bits 20MB/s 16
Ultra (Fast-20) IDC50, HD68 8 bits 20MB/s 8
Ultra Wide HD68 16 bits 40MB/s 8
Ultra2 (Fast-40) HD50, HD68 8 bits 40MB/s 8
Ultra2 Wide HD68, SCA 16 bits 80MB/s 16
Ultra160 HD68, SCA 16 bits 160MB/s 16
Ultra320 HD68, SCA 16 bits 320MB/s 16

Here are pictures of the connectors mentioned above. There is also some disorganized commentary below each picture; while I stand behind the information shown, it is by no means all-inclusive. It reflects information from my experiences which really only extend back to equipment manufactured around 1998. All of the photos were taken by me of my hardware and should not be reproduced without my permission.

IDC50

IDC50 male connector

IDC50 internal male connector. Most commonly used for internal CD-ROM drives, but also found on some hard drives (e.g., IBM DNES-318350). This is from an Adaptec 2940U HBA.

IDC50 female connector

IDC50 internal female connector. This particular cable was used to attach a SCA backplane to a CD-ROM. Notice that this cable is a flat (as opposed to twisted pair) ribbon cable.


HD50

HD50 female connector

HD50 external female connector. Used widely (along with the Centronics 50 connector) for external SCSI devices such as disk enclosures, CD-ROM drives, and similar peripherals. This is from an Adaptec 2940U HBA. Note that these connectors do not have screwholes to screw in the cable end.

HD50 male connector

HD50 external male connector on an external SCSI cable. Note that these connectors have springy clips rather than thumbscrews as are found in more contemporary connectors like VGA and DVI.


Centronics 50

Centronics 50 male connector

Centronics 50 male connector. This is used exclusively for external devices, and as far as I know, no HBAs exist which provide a C50 out. Thus, the connection between a controller and external device are usually made with a HD50(m)-C50(m) cable. C50-C50 cables are used to chain together multiple external devices. This interface is used for external disks, CD-ROMs, tape drives, et cetera.


HD68

external HD68 female connector

HD68 external female connector. Used widely for external SCSI devices such as disk arrays, tape drives, and similar peripherals. This particular one was on the back of a Sun Blade 1000.

external HD68 male connector

HD68 external male connector. This one is from a typical shielded external cable.

internal HD68 female connector

HD68 internal female connector. These are used to connect disks to the HBA. This one was from a Dell PERC2/SE card.

internal HD68 male connector

HD68 internal male connector. Although it is hard to see, this connector is on a twisted-pair ribbon cable.


SCA

SCA male connector

SCA male connector found on the back of a Seagate Cheetah ST336704LC disk. This interface is used chiefly on hot-swappable hard drives for use in servers and disk arays.

SCA female connector

This is the female component to the SCA connector. This is primarily found on backplanes such as the one pictured, which is from a Sun Enterprise 220R.

SCA female connector on cable

However, SCA has also been used to connect, via cable, on-board controllers to backplanes. The pictured cable has SCA female connectors on both ends and is from a Sun Enterprise 220R. I'm not terribly sure why this was done since the backplane is independently powered anyway. Notice that the cable is a flat ribbon (not twisted pair) since it was used to connect the backplane to the onboard Fast-40 controller.