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Single Connector Attachment, or SCA, is a type of connection for the internal cabling of Parallel SCSI systems. There are two versions of this connector: the SCA-1, which is deprecated, and SCA-2, which is the most recent standard. In addition there are Single-Ended and Low Voltage Differential types of the SCA.
SCA is no longer in widespread use, having been superseded by Serial attached SCSI.
Since hard disk drives are among the components of a server computer that are the most likely to fail, there has always been demand for the ability to replace a faulty 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, for example, this allows for seamless replacement of failed drives.
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 using jumpers on each drive. 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 SCA connector for parallel SCSI drives has 80 pins, as opposed to the 68 pin interface found on most modern parallel SCSI drives.