A hardware bus specification for connecting peripherals to a computer using a parallel transmission interface. The Small Computer System Interface (SCSI) was developed by Apple and is widely used in the PC world for high-end storage solutions. Microsoft Cluster Server (MSCS) uses a shared SCSI bus to provide failover support for two computers on which Microsoft Windows NT Server, Enterprise Edition is installed.
To implement SCSI on a system, you use a SCSI adapter to interface with the system bus, suitable SCSI devices such as SCSI hard drives, SCSI cables to daisy-chain the devices, and SCSI terminators for the ends of the bus. Each device on a SCSI bus must have a SCSI device ID number assigned to it, allowing SCSI to be used for daisy-chaining a number of devices together on a single parallel bus. You can change SCSI IDs by using dip switches or jumpers, or by using configuration software.
SCSI devices come in two basic types:
The SCSI interface comes in several varieties, including the following:
Graphic S-15. Four varieties of SCSI interface.
Eight-bit SCSI data paths are referred to as “narrow” paths, and 16-bit data paths are called “wide” paths.
SCSI cables must always be properly terminated in order for devices to be properly recognized; they should also use high-quality active terminators. Diagnostic terminators that help identify problems in signal quality are also available.
Always use the shortest cable possible for SCSI connections, because longer cables cause signals to weaken and are more affected by noise due to electromagnetic interference (EMI). When you calculate the total length of the SCSI bus, add the lengths of all the SCSI cable segments plus any internal SCSI cabling.
Be sure that all devices on a SCSI bus are configured for either single-ended or differential transmission - do not mix these methods on a single bus. You can connect single-ended devices to differential transmission devices only by using a signal converter. If you don’t use a signal converter, your SCSI devices might be damaged by unexpected voltages.