Disk Jumpers are tiny plastic blocks with metal inserts that are used for user configuration of IDE disk and CDROM drives. The jumpers short header posts together making a user determinable electrical contact. The most common arrangement on IDE drives is a three, five, or six pin header with one jumper that is used to set the drive as Master, Slave, or Cable Select (automatically select between Master and Slave based on which cable connector is used). Western Digital drives have traditionally differentiated between Stand alone Masters and Masters with slaves. Many drives have a usable default configuration if no jumper is present. Jumper positions on modern drives are usually indicated on the disk label. Prior to the mid-1990s, jumper positions had to be determined from the drive specification sheet.
Some drives have additional jumper blocks used for internal configuration options, e.g. which of several possible configuration the drive should report if interrogated by software. These usually should not be altered. Any user configurable settings will be given on the specification sheet.
SCSI drives will generally have configuration jumpers as well to select the SCSI device ID if nothing else. Some drives with built in terminations (used only for the end drive in a chain) may use a jumper to activate/deactivate the terminations.
Unused jumpers are often stored by pressing them down on only one pin of the pair or by connecting them sideways across two unused or grounded pins.
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Copyright 1994-2002 by Donald Kenney.