Document revision date: 30 March 2001
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OpenVMS Guide to Extended File Specifications

OpenVMS Guide to Extended File Specifications

Order Number: AA--REZRB--TE

April 2001

This document provides an overview of Extended File Specifications and describes the impact of Extended File Specifications on system managers, application developers, and users of the traditional OpenVMS environment.

Revision/Update Information: This manual supercedes the OpenVMS Guide to Extended File Specifications, 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, VAX, VMS, and the Compaq logo Registered in U.S. Patent and Trademark Office.

OpenVMS is a trademark of Compaq Information Technologies Group, L.P. in the United States and other countries.

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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.


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

Contents Index


Intended Audience

This document is intended for system managers, application developers, and users who implement Extended File Specifications on one or more systems in an OpenVMS environment.

Document Structure

This manual consists of the following chapters and appendixes:

Related Documents

For related information about Extended File Specifications, see the following documents:

For additional information about OpenVMS products and services, access the Compaq website at the following location: 

Reader's Comments

Compaq welcomes your comments on this manual. Please send comments to either of the following addresses:
Mail Compaq Computer Corporation
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Chapter 1
Overview of Extended File Specifications for OpenVMS

OpenVMS Version 7.2 on Alpha implements Extended File Specifications, which consists of two major components:

Taken together, these components provide much greater flexibility for OpenVMS Alpha systems (using Advanced Server for OpenVMS 7.2, formerly known as PATHWORKS for OpenVMS), to store, manage, serve, and access files that have names similar to those in a Windows 95/98 or Windows NT environment.

This chapter provides a brief overview of the benefits, features, and support for Extended File Specifications, as well as changes in OpenVMS behavior that occur under Extended File Specifications.

1.1 Benefits of Extended File Specifications

The deep directories and extended file names supported by Extended File Specifications provide the following benefits:

These benefits result from the features described in Section 1.2.

1.2 Features of Extended File Specifications

Extended File Specifications consists of two main features, the ODS-5 volume structure, and support for deep directories. These features are described in the sections that follow.

1.2.1 ODS-5 Volume Structure

OpenVMS Version 7.2 implements On-Disk Structure Level 5 (ODS-5). This structure provides the basis for creating and storing files with extended file names. You can choose whether or not to convert a volume to ODS-5 on your OpenVMS Alpha systems.

The ODS-5 volume structure allows the following features:

These features are described in the sections that follow. Long File Names

On an ODS-5 volume, the name of a file (excluding the version number) can be up to 236 8-bit or 118 16-bit characters long. Complete file specifications longer than 255 bytes are abbreviated by RMS when presented to unmodified applications.

For more information on extended file names, see Section 3.1.2. More Characters Legal Within File Names

A broader set of characters is available for naming files on OpenVMS. ODS-5 offers support for file names that use the 8-bit ISO Latin-1 character and 16-bit Unicode (UCS-2) character sets.

ISO LATIN-1 and Unicode (UCS-2) Character Sets

The ISO Latin-1 Multinational character set is a superset of the traditional ASCII character set used by versions of OpenVMS previous to Version 7.2. In extended file specifications, all characters from the 8-bit ISO Latin-1 Multinational character set are valid in file specifications, except the following:

C0 control codes (0x00 to 0x1F inclusive)
Double quotation marks (")
Asterisk (*)
Backslash (\)
Colon (:)
Left and right angle brackets (< >)
Slash (/)
Question mark (?)
Vertical bar (|)

To unambiguously enter or display certain special characters in an ODS-5 compliant file specification, such as a space, you must precede the character with a circumflex (^).

For more information on how these character sets are used in file names, see Section 3.1.2. Preservation of Case

In prior versions of OpenVMS, DCL, RMS, and the file system converted all file specifications to uppercase. ODS-5 preserves the case of file specifications. For example:

Directory  DISK1:[USER1] 

As you can see, the mixed-case of the file name is preserved.

For more information on case sensitivity, see Section

1.2.2 Deep Directory Structures

Both ODS-2 and ODS-5 volume structures support deep nesting of directories, subject to the following limits:

For example, a user can create the following deeply nested directory:

$ CREATE/DIRECTORY [.a.b.c.d.e.f.g.h.i.j.k.l.m] 

A user can create the following directory with a long name on an ODS-5 volume:


Complete file specifications longer than 255 bytes are abbreviated by RMS when presented to unmodified applications. Directory Naming Syntax

On an ODS-5 volume, directory names conform to most of the same conventions as file names when using the ISO Latin-1 character set. Periods and special characters can be present in the directory name, but in some cases, they must be preceded by a circumflex (^) in order to be recognized as literal characters.

Section 3.2 contains more information about deep directories. Section 3.6.1 contains information about displaying long directory names.

1.3 Considerations Before Enabling ODS-5 Volumes

ODS-5 is being introduced primarily to provide enhanced file sharing capabilities for users of Advanced Server for OpenVMS 7.2 (formerly known as PATHWORKS for OpenVMS), as well as DCOM and JAVA applications.

Once ODS-5 volumes are enabled, some of the new capabilities can potentially impact certain applications or layered products, as well as some areas of system management. The new syntax for file names that is allowed on ODS-5 volumes cannot be fully utilized on ODS-2 volumes. Because pre-Version 7.2 Alpha systems cannot access ODS-5 volumes, and Open VMS Version 7.2 VAX systems have limited ODS-5 functionality, you must be careful where and how you enable ODS-5 volumes in mixed-version and mixed-architecture OpenVMS Clusters.

The following sections comprise a summary of how enabling ODS-5 volumes can impact system management, users, and applications.

1.3.1 Considerations for System Management

RMS access to deep directories and extended file names is available only on ODS-5 volumes mounted on OpenVMS Alpha V7.2 systems. Compaq recommends that ODS-5 volumes be enabled only on a homogeneous OpenVMS Alpha V7.2 Cluster.

If ODS-5 is enabled in a mixed-version or mixed-architecture OpenVMS Cluster, the system manager must follow special procedures and be aware of specific restrictions on mixed-version and mixed-architecture OpenVMS Clusters with ODS-5 volumes enabled:

Section 1.3.2 describes in greater detail the limitations of ODS-5 support for users in a mixed-version or mixed-architecture OpenVMS Cluster.

Most unprivileged applications will work with most extended file names, but some may need modifications to work with all extended file names. Privileged applications that use physical or logical I/O to disk and applications that have a specific need to access ODS-5 file names or volumes may require modifications and should be analyzed. See the website for a list of fully supported OpenVMS applications. Section 1.3.3 describes in greater detail the impact of ODS-5 on OpenVMS applications.

Chapter 2 contains more information for determining the levels of support for Extended File Specifications, and guidelines for managing a system with ODS-5 volumes enabled.

1.3.2 Considerations for Users

A user on an OpenVMS Alpha Version 7.2 system can take advantage of all Extended File Specifications capabilities on ODS-5 volumes mounted on an OpenVMS Alpha Version 7.2 system.

A user on a mixed-version or mixed-architecture OpenVMS Cluster is subject to some limitations in ODS-5 functionality. Section lists those restrictions that exist on a mixed-version OpenVMS Cluster. Section lists those restrictions that exist on a mixed-architecture OpenVMS Cluster. Mixed-Version Support

Systems running prior versions of OpenVMS cannot mount ODS-5 volumes, correctly handle extended file names, or even see extended file names.

The following sections describe support on OpenVMS Version 7.2 and on prior versions of OpenVMS in a mixed-version cluster.

Users on OpenVMS Alpha Version 7.2 Systems

A user on an OpenVMS Alpha Version 7.2 system can continue to access pre-Version 7.2 files and directories; for example, a user can do all of the following:

Users on Pre-Version 7.2 Systems

On mixed-version clusters, some restrictions exist. Users on a version of OpenVMS prior to Version 7.2: Mixed-Architecture Support

Current ODS-2 volume and file management functions remain the same on both VAX and Alpha Version 7.2 systems; however, extended file naming and parsing are not available on VAX systems.

The following sections describe support on OpenVMS VAX and Alpha systems in a mixed-architecture cluster.

Limited Extended File Specifications Capabilities on VAX Systems

In mixed-architecture OpenVMS Version 7.2 clusters, OpenVMS Version 7.2 VAX systems are limited to the following Extended File Specifications functionality:

BACKUP Limitations

From a VAX system, users cannot successfully create or restore an ODS-5 image saveset. However, these users can successfully restore ODS-2-compliant file names from an ODS-5 saveset.

1.3.3 Considerations for Applications

ODS-5 functionality can be selected on a volume-by-volume basis. If ODS-5 volumes have not been enabled on your system, all existing applications will continue to function as before. If ODS-5 volumes have been enabled, you need to be aware of the following changes:

On ODS-5 volumes, existing applications and layered products that are coded to documented interfaces, as well as most DCL command procedures, should continue to work without modification.

However, applications that are coded to undocumented interfaces, or include any of the following, may need to be modified in order to function as expected on an ODS-5 volume:


All unmodified XQP applications running on an OpenVMS VAX or Alpha system that access an ODS-5 volume will see pseudonames returned in place of Unicode or ISO Latin-1 names that are not ODS-2 compliant. This can cause applications to act in an unpredictable manner.

Applications that specify or retrieve filenames with the XQP interface using ODS-5 disks must be modified in order to access files with extended names.

See Chapter 4 for further discussion of the support status of OpenVMS applications.

Next Contents Index

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