Terminators must be located at the very end of the bus. There are always two terminators per bus or bus segment. Also, many devices contain internal terminators that can be used in case the device is at one of the ends of the SCSI bus.
Different types of SCSI termination
Passive Termination: This is the oldest, simplest and the least reliable type of termination. It uses simple resistors to terminate the bus, similar to the way terminators are used on coaxial Ethernet networks. Passive termination is good for short, low-speed single-ended SCSI-1 buses but it is not at all suitable for any modern SCSI speeds and is rarely used today.
Active Termination: Adding voltage regulators to the resistors, used in passive termination, allow for more reliable and consistent termination of the bus. Active termination is the minimum required for any of the faster-speed single-ended SCSI buses.
Forced Perfect Termination (FPT): This is a more advanced form of active termination, wherein diode clamps are added to the circuitry to force the termination to the correct voltage. This virtually eliminates any signal reflections or any other problem and thereby provides the best form of termination of a single-ended SCSI bus.
High Voltage Differential (HVD): Buses that use high voltage differential signaling requires the use of special HVD terminators.
Low Voltage Differential (LVD): Newer buses that make use of low voltage differential signaling also need their own special type of terminators. In addition, there are special LVD/SE terminators designed for use with multimode LVD devices that can function in either LVD or SE modes. When the bus is running single-ended these behave like active terminators.
