A set of standards for connecting peripheral devices to computers. SCSI (pronounced ‘scuzzy’) is most commonly used with hard disks, but can connect a wide range of peripherals, such as printers and scanners. The standards are designed to be backwards-compatible so that older peripherals can still connect to newer computers. Current versions can support data-transfer rates of 640 megabits per second. SCSI has largely been replaced by USB in the personal computer market, but is still in widespread commercial use, especially on high-performance servers and storage systems. Early SCSI implementations were based on a parallel bus interface, but more recent versions use a serial approach because it is easier to set these up for very high-speed operation.