There have been a large variety of SCSI connectors in use at one time or another in the computer industry. Probably no computer interconnect (with the possible exception of RS-232 serial) has caused as much confusion. Twenty-five years of evolution and three major revisions of the standards resulted in requirements for Parallel SCSI connectors that could handle an 8, 16 or 32 bit wide bus running at 5, 10 or 20 Mbit/s, with conventional or differential signaling. Serial SCSI added another three transport types, each with one or more connector types. Manufacturers have frequently chosen connectors based on factors of size, cost, or convenience at the expense of compatibility.
SCSI often makes use of cables to connect devices together; in a typical example, a socket on a computer motherboard would have one end of a cable plugged into it, while the other end of the cable plugged into a disk drive or other device. This would mean that four connectors were involved in wiring the disk drive and computer together: the connector on the motherboard, the connectors at each end of the cable, and the connector on the disk drive. It is sometimes possible to have cables which have different types of connectors on them, and some cables can have as many as 16 connectors (allowing 16 devices to be wired together). Some types of connectors are typically used inside a computer or disk drive case, while others are used to connect a computer to a separate device such as a scanner or external disk drive.
Parallel SCSI allows for attachment of 16 devices to the SCSI bus, thus cables may have up to 16 connectors. It is unusual, however, for external cables (those that run between enclosures) to have more than 2.
While the female connector is slotted such that a cable with a matching keyed male connector can not be inserted upside-down, some manufacturers (including Sun Microsystems) supplied internal cables with male connectors that did not have the key, allowing for incorrect (and possibly damaging) connections.
In most cases, the controller would have a similar header-style connection. In some cases, though, the controller side of the cable would use a different connector. For example, in the Sun 260 series chassis (used for the Sun 3/260 and Sun 4/260 computers), the connector was the same 3-row 96-pin connector used to attach peripheral cards to the VMEbus backplane.
Most typically, external drive enclosures will have female connectors, while cables will have two male connectors. As with everything SCSI, there are exceptions.
Early SCSI interfaces commonly used a 50-pin micro ribbon connector. This connector is similar to the 36-pin connector used by Centronics for the parallel interface on their printers, thus the connector became popularly known as "Centronics SCSI" or "CN-50". It is also referred to as a "SCSI-1 connector"; since many connectors have been used for SCSI-1, this is can be confusing.
Apple used DB-25 connectors, which, having only 25 pins rather than 50, were less expensive to make, but compromised functionality. Further, DB-25s were commonly used for RS-232 serial cables and also to connect parallel printers, meaning that users might accidentally try to use completely inappropriate cables, since the printer and serial cables would fit the connector properly and be hard to visually distinguish. The DB-25's only advantage was that it was smaller than a CN50.
Digital Equipment Corporation mostly used the CN-50, but the VAXstation 3100 and DECstation 3100/2100 made use of a 68-pin connector on the rear of the workstation. This connector looks like it would be a high density Wide SCSI-2 connector, but is actually 8-bit SCSI-1.
Apple Macintosh laptops used a squarish external SCSI connector called an HDI-30 (High Density Interconnect) on the laptop itself (not on the peripheral end of the cable, unless two laptops were being connected together). These machines also had the interesting ability to become "SCSI slaves" (officially known as "SCSI Disk Mode" in Apple documentation), meaning that they could appear to be disk drives when attached to another computer's SCSI controller (a feature later reimplemented over FireWire for later, non-SCSI Mac hardware).
IBM's early RS6000 workstations sometimes used a "High Density Centronics" connector, which was a Centronics-style connector with smaller pins and shell. For some reason it had 60 pins, and is thus known as the "HDCN60"
Certain Japanese digital camera manufacturers wanted to put SCSI into their equipment, but conventional connectors would have been too large. Like IBM, they used a miniaturized Centronics connector, but this one had 50 pins, and was called the "HPCN50".
Some manufacturers used a DC-37 connector, often incorrectly referred to as a DB-37. These will most commonly be seen on three-cable systems, which are typically 16-bit or 32-bit "Wide SCSI" systems. Extra confusion is generated here since this connector was also frequently used with SMD disk drives, which are completely incompatible with SCSI drives.
Digital Equipment Corporation's StorageWorks products were one system of this type. DEC briefly allowed third parties to license this system, but reversed the decision after less than a year; as a result, third-party StorageWorks products are quite rare. Compaq also made a drive caddy system for the Proliant line of servers. Compaq purchased DEC, and Hewlett-Packard later purchased Compaq, and the Proliant and StorageWorks names were reused on other storage products, including later hot-swap systems.
Some of these caddy systems were OEM manufactured, which means that the same product could appear with numerous brand names and model identifications. These Hot-Plug drives in caddies generally use 80 pin connectors (HP,Compaq, DELL from SCSI-3 to Ultra-320)
Serial SCSI disk-drives have recently been introduced. They use smaller connectors due to the reduced number of signals required. There are three types of physical layer transports specified:
Additionally, there is the iSCSI transport, which is not present on the drives themselves, but is used to connect devices using TCP/IP networks. The drives themselves would use one of the other three connector types.
US Patent Issued to International Business Machines on Sept. 27 for "System and Method for Coupling a LTO HH Tape Device with a Serial Attached SCSI Connection to a Sas-Cable" (American, Japanese Inventors)
Oct 04, 2011; ALEXANDRIA, Va., Oct. 4 -- United States Patent no. 8,025,534, issued on Sept. 27, was assigned to International Business...