Specifications

OpenVMS VAX Operating System, Version 5.5-2 SPD 25.01.37
• Processor errors (these include processor soft errors,
processor hard errors, processor machine checks,
adapter errors).
• Memory errors are hardware errors that are handled
in a slightly different manner. The system examines
memory at startup time and does not use any pages
found to be bad. During system operation, the hard-
ware transparently corrects all single-bit memory er-
rors for those systems with ECC memory. An unre-
coverable error causes the memory page on which
the error occurred to be added to the bad page list.
If the page has not been modified, system operation
continues with a new copy of the page.
Other failures include:
• Operating system errors (system-detected inconsis-
tencies or architectural errors in system context)
• User errors
• I/O errors
The system logs all processor errors, all operating
system errors detected through internal consistency
checks, all double-bit memory errors (and a sum-
mary of corrected single-bit errors), and all I/O er-
rors. (Double-bit errors are detected only on those
VAX and Micro/VAX systems with ECC memory.)
If the system is shut down because of an unrecov-
erable hardware or software error, a dump of phys-
ical memory is written. The dump includes the con-
tents of the processor registers. The VMS System
Dump Analyzer utility is provided for analyzing mem-
ory dumps.
Power Failures
If power fails, the system shuts down automatically.
When power is restored, the system restarts automati-
cally and resumes processing at the point of interruption
if the system has a time-of-day clock and a memory bat-
tery backup unit, if the contents of memory are still valid,
and if the system is set to permit automatic rebooting.
The system restarts devices and communications lines.
All I/O operations in progress, including magnetic tape
I/O operations, are restarted. On request, programs can
be notified of power restoration. An optional battery-
operated hardware clock resets the date and time of day
when the system restarts. If the system does not have
a battery backup unit, or if the memory contents are
not valid on power restoration, the system will reboot
automatically if the system is set to permit automatic
rebooting.
If, for any reason, the system disk does not come back
on line after a power failure within a specific time after
the CPU regains power, the system shuts down.
Test Package and Diagnostics
VMS includes a User Environment Test Package
(UETP) that verifies that the VMS Operating System is
properly installed and ready for use on the customer’s
systems.
Diagnostics can be run on individual devices during nor-
mal system operation. Certain critical components can
operate in degraded mode. For example, the memory
cache can be disabled. The system places a compo-
nent in degraded mode when errors pass a threshold
level.
Input/Output
The QIO system service provides a direct interface to
the operating system’s I/O routines. These services are
available from within most VAX programming languages
and can be used to perform low-level I/O operations
efficiently with a minimal amount of system overhead
for time-critical applications.
Device drivers execute I/O instructions to transfer data
to and from the device and to communicate directly with
an I/O device. Each type of I/O device requires its own
driver. Digital supplies drivers for all devices supported
by the VMS Operating System and provides QIO system
service routines to access the special device dependent
features available in many of these devices. Users with
special needs or non-VMS supported devices can write
their own device drivers. The VMS Device Support Man-
ual and the VMS Device Support Reference Manual in
the VMS Extended Documentation set describe how to
write device drivers.
The VMS Operating System supports a variety of disk
and tape peripheral devices, as well as terminals, net-
works, mailboxes (virtual devices for interprocess com-
munication), and more general I/O devices. These I/O
devices include line printers, card readers, and general
purpose data acquisition devices such as the DRB32.
VMS Record Management Services (VMS RMS)
VMS RMS is a set of I/O services that help application
programs to process and manage files and records. Al-
though it is primarily intended to provide a comprehen-
sive software interface to mass storage devices, VMS
RMS also supports device-independent access to unit-
record devices.
VMS RMS supports sequential, relative, and indexed file
organizations in fixed-length and variable-length record
formats. VMS RMS also supports byte stream formats
for sequential file organization. VMS RMS record ac-
cess modes provide access to records in four ways:
sequentially, directly by key value, directly by relative
record number, and directly by record file address. VMS
RMS also supports block I/O operations for various
performance-critical applications that may require user-
defined file organizations and record formats.
8