IBM 3590 - Manual (Page 81)

so, the ACF indexes down the magazine until it finds the first cell with
a cartridge in the import position. The ACF sets the cell-status indicator
LED for that cell to in-use (steady green) and moves the cartridge from
the cell to the device.
2. If the ACF is disabled and in Automatic mode and a cartridge is placed
in the import position of the priority cell, the ACF is enabled. It then
loads the cartridge in the device, and sets the cell-status indicator LED
to in-use (steady green) for the priority cell.
3. If a cartridge is placed in the priority cell while the ACF is enabled and
in Automatic mode, the ACF sets the cell-status to in-use. The in-use
indicator LED of the priority cell is (steady green). When the ACF
completes its current operation, it automatically loads the priority cell as
described in step 2.
4. When a cartridge that was loaded while in Automatic mode is
unloaded, it is returned to its original cell, if possible. The in-use
indicator LED for that cell is then turned off. The ACF then searches the
magazine for the next cell in the import position and loads it in the
device. This process repeats until the ACF cannot find another cartridge
to load.
System Mode
System mode provides the operator an additional mechanism to keep the
drive continually loaded with cartridges from the magazine. When the ACF is
enabled, and the first cartridge loaded, subsequent load commands are under
the control of the attaching host. The ACF loads one cartridge in response to
each of these system commands until all the cartridges in the magazine are
processed.
System mode does not preclude specific mount requests from the attaching
host. The operator can supply specific cartridges to an application by inserting
the cartridge in the priority cell. The priority cell cartridge is automatically the
next cartridge to be loaded in the device, provided a load operation is not
currently in progress. When the specific cartridge is complete, the ACF
automatically resumes processing cartridges from the magazine under system
control.
Processed cartridges can be removed from the magazine, and unprocessed
cartridges can be added, without disturbing the ACF. The ACF locates each
unprocessed cartridge.
When the ACF is in System mode, the following applies (see also “ACF
Notes” on page 56):
v Initial conditions
– System mode must be selected from the SET ACF MODE menu.
Chapter 4. Automatic Cartridge Facility (ACF) and Magazine 61