User`s guide

LOAD
When to Load a Handler
Before you use a device in a foreground or system program, you must first load the
device handler since foreground programs cannot fetch. Also, if you have generated a
mapped monitor without fetchable handler support or if your handler is not fetchable,
you must load the device handler before it can be used. A fetchable handler is one
having the .FETCH programmed request enabling the monitor to load that handler.
RT–11 distributed monitors come with support for the .FETCH programmed request.
Devices Owned Exclusively by a Job
A device can be owned exclusively by either the foreground, background, or system
job. This exclusive ownership prevents other jobs from using the assigned device.
In the following example, the XL device is exclusively owned by VTCOM:
.LOAD XL=VTCOM
Different Units of a Device Owned by Different Jobs
Different units of the same random-access device controller can be owned by different
jobs. That is, DL1 can belong to the background job, while DL3 can belong to the
foreground or system job. If no ownership is indicated, the device is available for
use by any job.
NOTE
If you use the LOAD command to load a device handler,
and assign ownership of that handler to a job, all units
of that device become assigned to that job. This means
no other job can use any unit of that device.
Changing Job Ownership of a Device Handler
To change ownership of a device handler, use another LOAD command with the
=jobname parameter. The second LOAD command reassigns the ownership. It is
not necessary to first unload the device.
However, if you interrupt an operation that involves magtape, you must unload (with
the UNLOAD command) and then load the appropriate device handler (MM, MT, or
MS). When using these handlers with the FB monitor, this restriction does not apply.
Loading Units of the Same Type As the System Unit
You cannot assign ownership of the system unit (the unit you bootstrapped) of a
system device, and any attempt to do so is ignored. You can, however, assign
ownership of other units of the same type as the system device.
When Booting from a Diskette
If you booted from a diskette, loading the necessary device handlers into memory
can improve system performance significantly, since no handlers need to be loaded
dynamically from the diskette.
RT–11 Command Descriptions 177