How Vms Uses The Dssi Device Parameters - Digital Equipment VAX 4000 Model 100 Operator Instructions Manual

The FORCEUNI parameter controls the use of UNITNUM to override the
default device unit number supplied by the jumpers. When FORCEUNI is
set to a value of zero, the operating system uses the value assigned to the
UNITNUM parameter; when FORCEUNI is set to a value of one, the operating
system uses the value supplied by the jumpers.
The NODENAME parameter allows each device to have an alphanumeric node
name of up to eight characters. DSSI devices are shipped from the factory with
a unique identifier, such as R7CZZC, R7ALUC, and so on. You can provide
your own node name.
The SYSTEMID parameter provides a number that uniquely identifies the
device to the operating system. That parameter may need to be modified only
when replacing a device. Only Digital service representatives and licensed
self-maintenance customers should remove devices.
C.2 How VMS Uses the DSSI Device Parameters
This section describes how the operating system uses the parameters to form
unique identifiers for each device. Configurations that require you to assign
new unit numbers for devices are also described.
With an allocation class of zero, the operating system can use the default
parameter values to provide each device with a unique device name. The
operating system uses the node name along with the device logical name in the
following manner.
NODENAME$DIAu
where NODENAME is a unique node name, and u is the unit number.
With a nonzero allocation class, the operating system relies on unit number
values to create a unique device name. The operating system uses the
allocation class along with the device logical name in the following manner.
$ALLCLASS$DIAu
where ALLCLASS is the allocation class for the system and devices, and u is a
unique unit number.
Figure C–2 illustrates the need to program unit numbers for a system using
more than one DSSI bus and a nonzero allocation class. In the case of the
nonzero allocation class, the operating system sees three of the integrated
storage elements (ISEs) as having duplicate device names, which is an error,
as all unit numbers must be unique.
C–4 Programming Parameters for DSSI Devices