Single Connector Attachment, or SCA, is a type of connection for the internal cabling of SCSI systems. SCSI stands for Small Computer System Interface, and is a standard interface for transferring data between devices on a computer bus. ...

Since hard disk drives are among the components of a server computer that are the most likely to fail, there always has been a demand for a possibility to replace a erroneous drive without having to shut down the whole system. This technique is called hot-swapping and is one of the main motivations behind the development of SCA. In connection with RAID 5, for example, this allows for seamless replacement of failed drives. Hot swapping is the ability to add or remove parts of a computer system without turning off the system. ... Raid or RAID has several meanings: Redundant array of independent disks Raid bug spray The French elite police unit, Recherche Assistance Intervention Dissuasion A sudden, forcible entry by police A military operation or attack, air raid e. ...

Normally, hard disk drives make use of two cables: one for data and one for power, and they also have their specific parameters to be set in the BIOS of the system. Drives employing SCA only have one plug which carries both data and power and also allows them to receive their parameters from the host adapter. The plug for SCA has 80 pins, as opposed to the 68 pin interface found on most modern SCSI drives. Some of these pins on the host side are longer than others, so they are connected first and disconnected last. This ensures the electrical integrity of the whole system. Otherwise, the angle at which the plug is inserted into the drive could be the reason for damage because, for instance, the pin carrying the voltage could get connected before its corresponding ground reference pin.
To put another emphasis on their hot-plugging capability, SCA drives usually are installed into drive bays into which they slide with ease. 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. In computing, the Basic Input-Output System or BIOS is primitive software code embedded within a computer hardware system whose main functions are: to provide a visual display of the system to a monitor on startup of the system, have basic key access to a keyboard and provide low-level... In computer hardware a host adapter, as an interface device, connects a SCSI bus to a computer (the host). ... In the physical sciences, potential difference is the difference in potential between two points in a conservative vector field. ... The term ground (or earth) usually means a common return in circuits. ...

SCA is available both for the single-ended and low voltage differential flavours of SCSI. Low voltage differential signaling, or LVDS, is an electrical signalling system that can run at very high speeds over cheap, twisted-pair copper cables. ...