IBM 3590 - Manual (Page 49)

option
1 when there is no cartridge in the device. The Unload Drive option
2 shows the darker font, which indicates that it can be selected.
If you move the cursor ( ) to
1 and press Enter, the selection responds with
the normal font
2 momentarily. It then returns to the lighter font. The 3590
will not perform any action.
Figure 8. Example of Selectable Options
Chapter 3. Drive Operator Panel and Controls 29