This is the first of an ongoing series of column related to the technologies
relating to OpenVMS, its platforms, and related layered products and
This column is intended for the broad spectrum of OpenVMS
users, the people who support them, and the people who manage them. I will
emphasize the technological issues, and leave discussions relating to sales,
marketing, and related areas to others.
Please feel free to send questions and comments to me at
OpenVMS is, somewhat unique among operating systems for the
operational flexibility it offers. It is not unusual for even system
managers to go for years without needing to pay attention to which
physical drive an application is using. One of these distinguishing features is
the Logical Name facility, a vital, yet often under-appreciated guarantor
Logical names are pervasive in the OpenVMS environment. Relatively early in
the startup process (aspects of which will appear in a future column), the
system-wide logical name is initialized with a number of system-wide
logical names. The usage of SYS$SYSROOT is instructive.
SYS$SYSROOT is virtually the only place where the actual system device is
referenced by name (SYS$SYSDEVICE, SYS$COMMON, SYS$DISK, and SYS$SPECIFIC also
reference the physical name; for those who love detail, SYS$SYSDEVICE and
SYS$TOPSYS are actually combined to produce all of the other names during
the execution of the startup sequence).
The elegance of the approach is its simplicity. Almost without
exception, references are actually based on SYS$SYSROOT. Changes
in the operating environment (e.g. different disks, or separate directory
trees) only affect the value of SYS$SYSROOT (and its progenitors). This,
combined with a uniform API for mass storage devices, makes the actual
device configuration of the system virtually transparent to most of the
system and applications. For example, SYS$HELP is defined as
All of the logical names referenced so far are in the System Logical Name
Table. Most processes are associated with at least four logical name tables
(Process, Job, Group, and System). Names are generally translated by first
searching in hierarchical sequence the Process, Job, Group and System
tables. Advanced users can control the search and translation process.
Additionally, some translations preclude logical names defined by
end-users, for security and integrity reasons.
In the next installment, I will examine how these capabilities can be used
to advantage in user applications.
Next article in this series by Robert Gezelter:
Logical Names (Part 2) >>
Robert Gezelter is the Founding Principal of the consulting firm that bears
his name (www.rlgsc.com).
The consulting practice emphasizes in-depth technical expertise in computer
architectures, operating systems, networks, security, APIs, and related
matters. Mr. Gezelter has worked with OpenVMS since the initial release of
VAX/VMS in 1978.
His clients have ranged from small businesses to the Fortune 10
locally, nationally, and internationally.
He can be reached at