IBM 3590 - Manual (Page 33)

Fiducials
Figure 5 shows a B1A or E1A with a single fiducial
1 . The fiducial is used
by cartridge-handling devices to locate and remember where the tape
subsystem device is installed. Do not cover or change the fiducial.
Drive Power
The power switch is located on the back of each device. This toggle switch
controls the distribution of ac power to the associated device. Certain
subsystem configurations have additional controls for distribution of ac power
to the device.
It is recommended that all SCSI ports be taken offline before powering off the
drive. See “Services Menu” on page 33.
Indicators and Icons
This section describes the indicators on the 3590.
Figure 5. Library Locating Fiducials
Chapter 3. Drive Operator Panel and Controls 13