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Generally, and reflecting the order in which each type of terminator was introduced, unmarked terminators are passive, those marked only ''active'' are SE, and only those marked LVD (or SE/LVD) will correctly terminate an LVD bus and allow it to operate at full LVD speeds.
Some early disk drives included internal terminators, but most modern disk
There is a special case in SCSI systems that have mixed 8-bit and 16-bit devices where [[SCSI high byte termination|high-byte termination]] may be required.
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SCSI devices in the same SCSI transport family are generally [[backward compatibility|backward compatible]]. Within the parallel SCSI family, for example, it is possible to connect an Ultra-3 SCSI hard disk to an Ultra-2 SCSI controller. The interface operates at the lowest common supported standard, Ultra-2 in this case. Ultra-2, Ultra-160 and Ultra-320 devices may be freely mixed on the parallel [[LVDS|LVD]] bus with no compromise in performance.
===Mixing single
[[Single-ended signalling|Single-ended]] and [[LVDS]] devices can be attached to the same bus, but all devices will run at a slower, single-ended speed. The SPI-5 standard (which describes up to Ultra-640) deprecates single-ended devices, so some devices may not be electrically backward compatible.
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===Device IDs and termination===
Each parallel SCSI device (including the computer's [[host adapter]]) must be configured to have a unique SCSI ID on the bus. Another requirement is that any parallel SCSI bus must be terminated at both ends with the correct type of [[#Termination|terminator]]. Both active and passive terminators are in common use, with the active type much preferred (and required on LVD buses and Ultra SCSI). Improper termination is a common problem with parallel SCSI installations. In early SCSI buses, one had to attach a physical terminator to each end, but newer devices often have terminators built in, and the user simply needs to enable termination for the devices at either end of the bus (typically by setting a DIP switch or moving a jumper). Some later SCSI host adapters allow the enabling or disabling of termination through [[BIOS setup]]. Advanced SCSI devices automatically detect whether they are last on the bus and switch termination on or off accordingly.
===SCAM===
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