WWW Virtual Library for SCSI
The Small Computer Systems Interface
SCSI: Cable Overview
SCSI cables must be built according to the SCSI specifications. The latest information is found in Sections 5 and 6 of the SPI-2 document of the SCSI-3 specifications. SCSI cables for external use should consist of 25 or 34 twisted pairs of multi-stranded flexible copper wires. It should be double shielded and the cable shield must be connected to the shell of the connectors, but not to any of the ground lines of the SCSI signals. The nominal differential impedance of the cable used should be 110 to 135 Ohms. It is very important that SCSI signal pairs are assigned to wire pairs as demanded by the SCSI standard: REQ and ACK in the center, control lines in the middle and data lines at the outside of the cable. Cables meeting the requirements for higher data transfer rates improve margins for lower data transfer rates.
|Pictures of SCSI Connectors From STA's Site|
Common SCSI Bus Connectors
Table courtesy of Paralan Corp and Quantum Corp.
|Host or Host Adapter||Connector|
|This 50-contact, centronics-type, ribbon contact connector is used for Slow, Fast or Ultra, 8-bit Narrow SCSI applications. Frequently called the "SCSI-1 Connector". The SCSI spec terms it the "Alternative 2, A-cable connector".|
|This DB-50 pin-and-socket connector is not recognized by the SCSI specifications. Used on older Sun and DG computers for 8-bit Narrow SCSI applications.|
|Known as the 50-pin high-density SCSI connector. This pin-and-socket connector is also called the "SCSI-2 Connector". The SCSI recognized version has "latch" type fasteners. Used for 8-bit Narrow SCSI devices. The SCSI spec terms it the "Alt 1, A-cable connector".|
|This pin-and-socket DB25 connector was used on Apple computers, devices directed at the Apple market and some older Sun workstations. Not recognized by the SCSI specs. SCSI systems with this connector must be limited to Slow data rates and be no more than 4 or 5 feet long.|
|Known as the 68-pin high-density SCSI connector. This pin-and-socket connector is also called the "SCSI-3 Connector". The SCSI recognized version has "thumbscrew" fasteners. A few SCSI devices have used the "latch" version. Used for 16-bit Wide SCSI devices. The SCSI spec terms it the "Alt 3, P-cable connector".|
|This 68-contact, ribbon type connector is known as the "VHDCI" SCSI connector. Its very small size allows fitting up to 4 of them on the mounting bracket on the back of a PCI or ISA bus card. The SCSI spec terms it the "Alt 4, P-cable connector".|
(All drawings are views of the female connector -- the one that is normally mounted on the SCSI device.)
SCSI Cables and Cable Testers
Guide to SCSI Cables Some of the common SCSI connections.
L-com Connectivity Products Variety of cables includes USB, computer, coaxial, audio and video cables and assemblies, Fiber Optic and network equipment.
Cabling Frequently Asked Questions by Peter Macaulay Document for the comp.dcom.cabling newsgroup. Topics covered include the types of cables (fiber, coax, copper, unshielded twisted pair-UTP, shielded twisted pair), installation techniques, standards as well as fire and building safety codes.
Paralan SCSI Quiet Cable™ is available for wide and narrow SCSI with any combination of Centronics, DB50 and 50/68-pin sub minature D-type connectors. Also in customer specified lengths from 0.3 to 50 m (1 to 160 feet).
CS Electronics CyberConnection From lap-tops to mainframes, specializing in SCSI data cables for any subsystem. For all versions of SCSI, RAID and fibre channel.
Curtis Connections Manufacturer and distributor of computer cable connectivity products to vars, retailers, distributors, and wholesalers. Cables and adapters for every leading platform including IBM/PC, Macintosh, Workstation, SCSI, and network applications in the US, Taiwan and China.
Granite Digital High performance SCSI external diagnostic cables, SCSI active diagnostic terminators, SCSI active switch boxes/repeaters, custom teflon and olefin internal cables, SCSI cable testers, and other high performance accessories.
Interconnect Solutions Inc. Manufacturer of high speed, state-of-the-art interconnect products, for the mass Storage and NAS marketplace. Cable assemblies, interface adapters, and terminators.
Ram Electronic Industries Computer cables, all types, SCSI cables, Ultra2 cables, USB cables and hubs, internal hard drive, network cables (CAT5 patch cables, Ethernet,Token-Ring) plus computer accessories.
Scistuff.com SCSI cables and accessories. Custom internal cabling built to your specs.
SCSI cables Computer cables, switch boxes. SCSI Cables, internal cables, HPDB68, custom Cables, and cables for OEM.
SCSI Masters.com SCSI manufacturer and distributor of cables, custom cabling and terminators.
SCSI4PC Sells SCSI adapter, terminator and cables for all types of bus interfaces. Also extra long and hard to find cable.
SR Components, Inc. Computer cables, SCSI cables, and category 5 patch cable.
Timbercon Distributor of Computer Cables for Apple, Sun, SCSI Devices, Fiber Optics, and Custom Cables.
Cirris Systems Easy to use cable testers, harness testers, and hipot testers.
Eclipse Tools Cable testers for most common PC cables, including SCSI.
ST123 SCSI Cable Tester Tests SCSI cables in seconds, checks for twisted pair integrity as well as shorts, opens, and pin-to-pin continuity, removing ninety percent of most external SCSI- based device problems.
Cables N Mor Computer cable including SCSI, Null Modem, MIDI, USB, IEEE 1284 printer, joystick, and networking cable.
Computer Cable Makers, Inc. Cables for all versions of SCSI, adapters, CAT-5 and fiber.