Document revision date: 30 March 2001
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OpenVMS Programming Concepts Manual

OpenVMS Programming Concepts Manual

April 2001

This manual describes the features that the OpenVMS operating system provides to programmers.

Revision/Update Information: This manual supersedes the OpenVMS Programming Concepts Manual, Version 7.2.

Software Version: OpenVMS Alpha Version 7.3
OpenVMS VAX Version 7.3

Compaq Computer Corporation
Houston, Texas

© 2001 Compaq Computer Corporation

Compaq, AlphaServer, VAX, VMS, and the Compaq logo Registered in U.S. Patent and Trademark Office.

Alpha, OpenVMS, PATHWORKS, DECnet, and DEC are trademarks of Compaq Information Technologies Group, L.P.

UNIX and X/Open are trademarks of The Open Group in the United States and other countries.

All other product names mentioned herein may be the trademarks or registered trademarks of their respective companies.

Confidential computer software. Valid license from Compaq required for possession, use, or copying. Consistent with FAR 12.211 and 12.212, Commercial Computer Software, Computer Software Documentation, and Technical Data for Commercial Items are licensed to the U.S. Government under vendor's standard commercial license.

Compaq shall not be liable for technical or editorial errors or omissions contained herein. The information in this document is provided "as is" without warranty of any kind and is subject to change without notice. The warranties for Compaq products are set forth in the express limited warranty statements accompanying such products. Nothing herein should be construed as constituting an additional warranty.

Printed in the U.S.A.


The Compaq OpenVMS documentation set is available on CD-ROM.

This document was prepared using DECdocument, Version V3.3-1e.

Contents Index


Intended Audience

This manual is intended for system and application programmers. It presumes that its readers have some familiarity with the OpenVMS programming environment.

Document Structure

The following chapters provide information about the programming features of the OpenVMS operating system. A list of the chapters and a summary of their content is as follows:

Related Documents

For a detailed description of each run-time library and system service routine mentioned in this manual, see the OpenVMS Run-Time Library documentation and the OpenVMS System Services Reference Manual.

You can find additional information about calling OpenVMS system services and Run-Time Library routines in your language processor documentation. You may also find the following documents useful:

For additional information about OpenVMS products and services, access the following World Wide Web address: 

Reader's Comments

Compaq welcomes your comments on this manual. Plese send comments to either of the following addresses:
Mail Compaq Computer Corporation
OSSG Documentation Group, ZKO3-4/U08
110 Spit Brook Rd.
Nashua, NH 03062-2698

How To Order Additional Documentation

Use the following World Wide Web address to order additional documentation: 

If you need help deciding which documentation best meets your needs, call 800-282-6672.


The following conventions are used in this manual:
Ctrl/ x A sequence such as Ctrl/ x indicates that you must hold down the key labeled Ctrl while you press another key or a pointing device button.
PF1 x A sequence such as PF1 x indicates that you must first press and release the key labeled PF1 and then press and release another key or a pointing device button.
[Return] In examples, a key name enclosed in a box indicates that you press a key on the keyboard. (In text, a key name is not enclosed in a box.)

In the HTML version of this document, this convention appears as brackets, rather than a box.

... A horizontal ellipsis in examples indicates one of the following possibilities:
  • Additional optional arguments in a statement have been omitted.
  • The preceding item or items can be repeated one or more times.
  • Additional parameters, values, or other information can be entered.
A vertical ellipsis indicates the omission of items from a code example or command format; the items are omitted because they are not important to the topic being discussed.
( ) In command format descriptions, parentheses indicate that you must enclose choices in parentheses if you specify more than one.
[ ] In command format descriptions, brackets indicate optional choices. You can choose one or more items or no items. Do not type the brackets on the command line. However, you must include the brackets in the syntax for OpenVMS directory specifications and for a substring specification in an assignment statement.
| In command format descriptions, vertical bars separate choices within brackets or braces. Within brackets, the choices are optional; within braces, at least one choice is required. Do not type the vertical bars on the command line.
{ } In command format descriptions, braces indicate required choices; you must choose at least one of the items listed. Do not type the braces on the command line.
bold text This typeface represents the introduction of a new term. It also represents the name of an argument, an attribute, or a reason.
italic text Italic text indicates important information, complete titles of manuals, or variables. Variables include information that varies in system output (Internal error number), in command lines (/PRODUCER= name), and in command parameters in text (where dd represents the predefined code for the device type).
UPPERCASE TEXT Uppercase text indicates a command, the name of a routine, the name of a file, or the abbreviation for a system privilege.
Monospace text Monospace text indicates code examples and interactive screen displays.

In the C programming language, monospace type in text identifies the following elements: keywords, the names of independently compiled external functions and files, syntax summaries, and references to variables or identifiers introduced in an example.

- A hyphen at the end of a command format description, command line, or code line indicates that the command or statement continues on the following line.
numbers All numbers in text are assumed to be decimal unless otherwise noted. Nondecimal radixes---binary, octal, or hexadecimal---are explicitly indicated.

Chapter 1
Overview of Manuals and Introduction to Development on OpenVMS Systems

This chapter describes the structure of this two-volume manual. This chapter also provides an overview of the OpenVMS operating system, its components, and the tools in programming software.

1.1 Overview of the Manual

This two-volume manual introduces the resources and features of the OpenVMS operating system that are available to help you develop programs. Table 1-1 describes the parts of each volume.

Table 1-1 Manual Description
Volume Part Description
Volume I    
  Part I Process and Synchronization. Describes the creation, communication, and control of processes. It also describes symmetric multiprocessing (SMP), and the synchronizing of data access, programming operations, and access to resources.
  Part II Interrupts and Condition Handling. Describes the use of asynchronous system traps (ASTs), and the use of routines and services for handling conditions.
  Part III Addressing and Memory Management. Describes 32-bit and 64-bit address space, and the support offered for 64-addressing. It also provides guidelines for 64-bit application programming interfaces (APIs); and OpenVMS Alpha, VAX, and VLM memory management with run-time routines for memory management, and alignment on OpenVMS Alpha and VAX systems.
  Part IV Appendices: Macros and Examples of 64-Bit Programming. Describes the macros used in 64-bit programming, along with two examples of 64-bit programmming.
Volume II    
  Part I OpenVMS Programming Interfaces: Calling a System Routine. Describes the basic calling format for OpenVMS routines and system services. It also describes the STARLET structures and definitions for C programmers.
  Part II I/O, System and Programming Routines. Describes the I/O operations, and the system and programming routines used by run-time libraries and system services.
  Part III Generic Macros for Calling System Services. Describes in appendices the generic macros used for calling system services, OpenVMS data types, and the distributed name services on OpenVMS VAX systems.

1.2 Overview of the OpenVMS Operating System

The OpenVMS operating system is a highly flexible, general-purpose, multiuser system that supports the full range of computing capabilities, providing the high integrity and dependability of commercial-strength systems along with the benefits of open, distributed client/server systems.

OpenVMS operating systems can be integrated with systems from different vendors in open systems computing environments. Compaq has "opened" the traditional VMS system to support software that conforms to international standards for an open environment. These industry-accepted, open standards specify interfaces and services that permit applications and users to move between systems and allow applications on different systems to operate together.

The OpenVMS operating system configuration includes OpenVMS integrated software, services and routines, applications, and networks. The system supports all styles of computing, from timesharing to real-time processing to transaction processing. OpenVMS systems configured with optional software support distributed computing capabilities and can function as servers in multivendor client/server configurations.

The OpenVMS operating system is designed to provide software compatibility across all the processors on which it runs:

Both VAX and Alpha processors encompass a wide range of computing power: from desktop and deskside workstations, through distributed office systems and data center servers, to extremely high performance enterprisewide servers.

The following sections describe the components of the OpenVMS operating system, give a general overview of the system software, and describe the various styles of computing that OpenVMS software supports. The sections also summarize the basic ways in which OpenVMS software can be configured and connected to other software, and the hardware platforms and processors on which the OpenVMS software runs.

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