On the VAX, devices in NEXUS slots are normally noted, thus memory controllers, UNIBUS and MASSBUS adaptors. Devices which are not supported which are found in NEXUS slots are noted also. The Q-bus on the MICROVAX is configured in the same way as the UNIBUS.
MASSBUS devices are located by a very deterministic procedure since MASSBUS space is completely probe-able. If devices exist which are not configured they will be silently ignored; if devices exist of unsupported type they will be noted.
UNIBUS devices are located by probing to see if their control-status registers respond. If not, they are silently ignored. If the control status register responds but the device cannot be made to interrupt, a diagnostic warning will be printed on the console and the device will not be available to the system.
Normally, the system uses the disk from which it was loaded as the root
filesystem.
If that is not possible,
a generic system will pick its root device
as the
``best''
available device
(MASSBUS
disks are better than
SMD UNIBUS
disks are better than
RK07s;
the device must be drive 0
to be considered).
If such a system is booted with the
RB_ASKNAME
option (see
reboot(2)),
then the name of the root device is read from the console terminal at boot
time, and any available device may be used.
hp0
'',
for tape formatters
like
``
ht1
''.
The drive number comes from the unit plug on the drive
or in the
TM
formatter
(not
on the tape drive; see below).
tu0
at
ht0
slave
0
'',
where
``
tu0
''
is the name for the tape device and
``
ht0
''
is the name
for the formatter. A tape slave was found on the tape formatter at the
indicated drive number (on the front of the tape drive).
UNIX
will call the device, e.g.,
``
tu0
''.
dz0
''
was found on
`uba%d'
at control-status register address
`%o'
and with
device vector
`%o'.
The device interrupted at priority level
`%x'.
up0
at
sc0
slave
0
'',
where
``
up0
''
is the name of a disk drive and
``
sc0
''
is the name
of the controller. Analogous to
MASSBUS
case.