SCSI connector
Generally, two connectors, designated male and female, plug together to form a connection which allows two components, such as a computer and a disk drive, to communicate with each other.
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 megatransfer/s, with conventional or differential signaling.
Manufacturers have frequently chosen connectors based on factors of size, cost, or convenience at the expense of compatibility.
Early generations of SCSI hard drive assemblies generally had two connectors (power and communication).
This type of header was used in a typical desktop PC until around 2010, including the 40-pin (two rows of 20) version used for ATA fixed and optical disk drives.
[citation needed] This connector includes a power connection and also has long and short pins which enable hot swapping.
Digital Equipment Corporation mostly used the CN-50, but the VAXstation 3100 and DECstation 3100/2100 made use of a MALE 68-pin connector on the rear of the workstation.
Certain Japanese digital camera manufacturers wanted to put SCSI into their equipment, but conventional connectors would have been too large.
[1] A few vendors did use the Micro Centronics 50, also known as Mini Delta Ribbon,[2] and IBM continued to use the HDCN60 on some RS-6000 systems.
The Amplimite and MDR connectors are similar in shape and size, but can be distinguished by the former using pin contacts and the latter using wipers.
Similarly, connecting a single-ended device (SE) onto a LVD SCSI chain will cause the bus to fall back to single-ended mode, removing the ability to run faster than Ultra speed (20 MHz) and possibly causing an unstable bus for exceeding SE limits.
Some of these systems allowed for hot swap (drives could be replaced with the system running), while others allowed "warm swap", in which the SCSI bus was "quiesced" (meaning all drive activity was stopped) but remained powered on with devices ready.
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.
Some of these caddy systems were OEM manufactured, which means that the same product could appear with numerous brand names and model identifications.
In addition there are Single-Ended (SE) and Low Voltage Differential (LVD) types of the SCA.
Normally, hard disk drives make use of two cables: one for data and one for power, and they also have their specific parameters (SCSI ID etc.)
Drives employing SCA have only one plug which carries both data and power and also allows them to receive their configuration parameters from the SCSI backplane.
The additional length also provides what is known as a pre-charge which provides a means whereby the device is alerted to a pending power surge.
At the far end of these bays is the backplane of the SCSI subsystem located with a connector that plugs into the drive automatically when it is inserted.
Serial SCSI disk-drives use smaller connectors due to the reduced number of signals required.
