Master/Slave (M/S)

Also known as Dual Drive Support. Two drives may be accessed via a common interface cable, using the same range of I/O addresses. The drives are jumpered as device 0 or 1 (Master/Slave), and are selected by the drive select bit in the Device/Head register of the task file.

All task file registers are written in parallel to both drives. The interface processor on each drive decides whether a command written to it should be executed; this depends on the type of command and which drive is selected. Only the drive selected executes the command and activates the data bus in response to host I/O reads; the drive not selected remains inactive.

A Master/Slave relationship exists between the two drives; device 0 is the Master and device 1 is the Slave. When M/S jumper is closed (factory default), the drive assumes the role of Master; when open the drive acts as a Slave. In single drive configurations, the M/S jumper must be closed. On older 7000 series drives the M/S jumper is J20 (check the drive specification sheet for the exact location). On the newer 80000 series drives, the M/S jumper is J50 and it is located on the back of the drive between the J1 EIDE connector and the J2 power connector.

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