The OpenVMS Frequently Asked Questions(FAQ)

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9.6 What is the maximum file size, and the RMS record size limit?

RMS can store individual files of a size up to the maximum supported volume size. Under OpenVMS V6.0 and later, the volume size and the RMS maximum file size limit is 2**31 * 512 bytes---one terabyte (1 TB).

"Use a volume set to provide a large, homogeneous public file space. You must use a volume set to create files that are larger than a single physical disk volume. (The file system attempts to balance the load on the volume sets, for example, by creating new files on the volume that is the least full at the time.)"

"You can add volumes to an existing volume set at any time. The maximum number of volumes in a volume set is 255."

The RMS formats---sequential, relative, and indexed---are limited by the one terabyte maximum volume size. RMS relative files are further limited to a number of records that will fit in 32 bits---4 billion records. Sequential and indexed formats do not have a record limit.

Also see Section 2.16.1, Section 14.26.

9.7 How do I write CD-Recordable or DVD media on OpenVMS?

How to create CD-R, CD-RW, DVD-R, DVD+R, DVD-RW, or DVD+RW media on OpenVMS?

Alternatively, consider the following command on OpenVMS Alpha V7.3-1 and later:


While folks have had success getting PC-based CD-R/RW or DVD-R/RW or DVD+R/RW tools to work with OpenVMS partitions, it is far easier and more reliable to use the OpenVMS-based versions of these tools and directly-attached devices.

More details: Creation of CD recordable or DVD recordable media under OpenVMS typically involves one of two approaches: the use of the optional CD-R (`Scribe') capabilities available for the InfoServer or other "offline" hardware packages (PC-based packages will be included in this), or the use of a host-based package such as the CDRECORD or CDWRITE13_VMS or other utilities, OpenVMS ports of common open-source tools made available by Dr. Eberhard Heuser-Hofmann and others. Dr. Heuser-Hofmann has DVDwrite , a commercial package which can record DVD media. (

OpenVMS can read ODS-2, ODS-5, and ISO-9960 format CD-ROMs. (If you are very careful, you can create a dual-format CD-R; a CD-R with both ODS-2 and ISO-9660 or both ODS-5 and ISO-9660 or both.)

InfoServer hardware configurations are no longer available from HP, but may potentially be acquired through other means; as used equipment.

Packages related to the use of DVD archiving are also available, see the multi-volume capabilities of the DVDarchive/restore Freeware. 

Additional information is available at the following sites:

U.S. Design offers a package that includes the tools necessary to create a CD or DVD-R with either ISO-9660 or ODS-2 format, for standalone CD-R/RW, DVD-R, or DVD+R/RW drives, for recent OpenVMS versions. Details are available at:

Also see Section 9.7.2 for details on access to recorded media on older CD-ROM drives.

9.7.1 CD and DVD notation, terminology?

CD-ROM is pre-recorded Compact Disk media, and is the original and oldest CD format. The original CD media was physically stamped, a recording process that is now largely reserved to the highest-volume media reproduction requirements.

CD-R is CD Recordable, a write-once storage medium that can be read by all but the oldest of CD drives; a format which can be read and often even recorded by most CD-RW drives.

CD-RW is CD ReWritable, a format which is readable by many CD drives and by most CD-R drives, and with media that can be recorded and re-recorded by CD-RW drives.

CD media recording speeds are listed as multiples of 150 kilobytes per second, so a 10X drive records at 1500 kilobytes (1.5 megabytes) per second. 600 MB (70 minutes) and 700 MB (80 minutes) recording capacities are both widely available. The minutes designation is derived from the traditional audio-format recording capacity of the particular media.

DVD-R/RW is the older of two common Digital Versatile Disk recording formats, and the DVD-R Recordable or DVD-RW ReWritable media can be read by many DVD drives. As with CD-R formats in older CD drives, older DVD and particularly first-generation DVD players may have problems reading this media format.

DVD+R/RW is the newer of the two common Digital Versatile Disk recording formats, and the DVD+R Recordable or DVD+RW ReWritable media can be read by many DVD drives. Akin to DVD-R/RW media, older and particularly first-generation DVD drives can have problems reading this media format.

The DVD Plus-series drives and media tend to record faster than Minus drives, as (as of this writing) the Plus (+) drives do not require an initial media formatting pass and the Minus (-) drives do. While the appropriate Plus (+) or Minus (-) DVD raw media must be chosen for the particular DVD recorder (and DVD recording drives that are compatible with and capable of using both Plus and Minus media are available), the resulting recorded media is generally readable (playable) in all recent DVD drives and DVD players, regardless of type. (Compatibility is best within the same media-series devices of course, but be certain to verify compatibility across devices regardless of the particular device or particular recording media chosen.)

Presently Plus (+) media is slightly more expensive than Minus (-), but with the prices of all CD and all DVD media continuing to consistently fall, the differences in DVD media costs are becoming irrelevent for all but the production of huge volumes of DVD media.

The rated DVD recording speeds are in multiples of 1353 kilobytes per second, thus a DVD 1X drive is roughly equivalent to a CD 9X drive in I/O requirements and transfer speed.

DVD drive recording speed can and does vary. DVD disk drive recording speed is limited by the rated recording speed of the media used, so the slower (and cheaper) DVD media will not record any more quickly in a faster drive. A 2.4X DVD drive loaded with 1X media will record at 1X.

9.7.2 Use of RRD42 and other older (embossed-media) CD drives?

The RRD42 series SCSI CD-ROM drive is sufficiently old that it can have problems processing CD-R and CD-RW media. Other very old CD drives can have equivalent media compatibility problems when attempting to read (much) newer CD media and newer CD media technologies. These older CD drives are generally intended for use with the so-called embossed media, rather than with non-embossed recorded (recordable) media now in common circulation.

Please consider using a slightly-less-ancient CD-ROM or CD-R or CD-RW drive when working with non-embossed recorded CD media.

To paraphrase one knowledgable---though deliberately nameless---storage engineer, "The RRD42 drive is just past the drooling idiot stage".

9.8 What I/O transfer size limits exist in OpenVMS?

The maximum transfer size is an attribute of the particular I/O device, controller and driver combination; there is no inherent limit imposed by OpenVMS (other than the fact that, today, byte counts and LBNs are generally limited to 32 bits).

The maximum size of a device I/O request is limited by the value in UCB$L_MAXBCNT, which is set by the device driver based on various factors. (Also check the setting of the MAXBUF system parameter for buffered I/O transfers, and check the process quotas.)

Currently, SCSI drivers limit I/O transfers to FE00(16) bytes, 65024 bytes (decimal). The reasons for this transfer size limitation are largely historical. Similarly, DSSI devices are limited to the same value, this for hardware-specific reasons. Transfers to HSC and HSJ device controllers via the CI are limited to 1,048,576 bytes. Client MSCP-served devices are limited to 65535 bytes---to help ensure that the I/O fragmentation processing happens on the client and not on the server system.

Parts of the OpenVMS I/O subsystem are optimized for data transfers less than 64KB, because (obviously) most I/O operations are (substantially) less than that. OpenVMS can handle larger transfers, if the driver and the device can handle it.

Also see Section 9.4, Section 9.5.

9.9 Can I use ODBC to connect to OpenVMS database files?

Yes, you can use various available third-party packages that permit remote ODBC clients to access RMS files and various commercial databases via the network.

For RMS, consider acquiring one of the packages available from EasySoft, Attunity Connect (formerly known as ISG Navigator), Oracle (DB Integrator), SolutionsIQ, and Synergex.

For specific commercial databases (other than RMS, of course), contact the database vendor directly for assistance.

9.10 If my disks are shown as VIOC Compatible, am I using XFC?

Yes, you are using XFC caching.

Disks that are using XFC caching use communication and coordination protocols that are compatible with the older VIOC caching implementation. With the initial implementation of XFC on OpenVMS, you can use the command SHOW MEMORY/CACHE to see no disks reported in full XFC mode; all disks shown will be listed in "VIOC Compatable Mode".

If you have the OpenVMS system parameter VCC_FLAGS set to 2 and are using OpenVMS Alpha V7.3-1 or later, or are using OpenVMS Alpha V7.3 with the VMS73_XFC V2.0 ECO kit or later or with the UPDATE kits, you are using XFC.

Another confusion: the XFC product version is and remains V1.0 in all released configurations, please do not confuse the internal XFC product version (displayed by various commands) with the version number associated with the various ECO kit(s). XFC V1.0 does not permit volumes to enter full XFC caching, as displayed by the "Vols in Full XFC mode" portion of the DCL command SHOW MEMORY/CACHE output.

Chapter 10
OpenVMS Programming Information

10.1 Modular Programming, Facility Prefixes and Symbol Naming?

Please first review the OpenVMS Programming Concepts Manual and the Guide to Modular Programming manuals. Both are available within the OpenVMS documentation set, and provide details of the expected norms for OpenVMS programs.

OpenVMS provides a registry for facility prefixes and for MESSAGE message compiler codes. To request a prefix and a message facility code for a product you are reselling, send your request in a mail message addressed to product[-at-sign-], requesting the submission form and details of the registration process.


Please do not request facility prefixes for products that local to your business, your site, or your system. Facility prefixes and message codes and the facility registration process are intended solely for HP products and Partner Products (and yes, even OpenVMS Freeware packages) that will be distributed across multiple OpenVMS customer sites.

For a list of common coding bugs, please see the remainder of this section of the FAQ and specifically Section 10.22, please also see the Ask The Wizard topic (1661), and for information on debugging an OpenVMS application, please see topic (7552).

For additional information on the OpenVMS Ask The Wizard (ATW) area and for a pointer to the available ATW archive, please see Section 3.9.

10.2 Can I have a source code example of calling...?

Please use the available SEARCH command on OpenVMS, and please remember to search the available resources, including the support databases and the newsgroup archives. Please also realize that most OpenVMS system services use similar calling sequences, meaning that an example of calling sys$getjpi can be used as an example for sys$getsyi and sys$getdvi. Students: please do not expect folks to write your homework for you. As for search resources:

OpenVMS programming documentation, including the numerous example programs found in recent versions of the OpenVMS Programming Concepts manual, is available:

As for details of argument passing, most OpenVMS system services and RTL routines pass string arguments by descriptor. Languages which support native string data types create descriptors automatically; those which do not (eg., C) require that you set them up explicitly. For further details on using descriptors and particularly for using descriptors from C, please see Section 10.13.

There is extensive information available on how to call OpenVMS system services and OpenVMS Run-Time Library routines, including examples in numerous languages. Among the best available references are:

In addition, if you are a subscriber to the HP Software Information Network (available to those with a software support contract), the support database contains hundreds of worked examples of calling system services and RTL routines, including the one that seems to trip up almost everyone, SMG$CREATE_MENU.

Arne Vajhøj has put together a collection of OpenVMS example programs. It can be found at:

Additional information and examples for OpenVMS are available via:

For additional information on the OpenVMS Ask The Wizard (ATW) area and for a pointer to the available ATW archive, please see Section 3.9. and via:

10.3 How do I get the arguments from the command line?

If you're writing a program and want to accept arguments from a foreign command, you can use LIB$GET_FOREIGN to get the command line and parse it yourself, or if you're programming in C, use the normal argc/argv method.

To write an application which uses the normal DCL verb/qualifier/parameter syntax for invocation, see the description of the CLI$ routines in the OpenVMS Callable Utility Routines Reference Manual.

It is possible to write an application which can be used both ways; if a DCL verb isn't used to invoke the image, the application parses the command line itself. One way to do this is to call CLI$GET_VALUE for a required parameter. If it is not present (or you get an error), call LIB$GET_FOREIGN to get the command line and do the manual parse.

See also Section 8.1.

10.4 How do I get a formatted error message in a variable?

Use the SYS$PUTMSG system service with an action routine that stores the message line(s) in the variable of your choice. Be sure the action routine returns a "false" (low bit clear) function value so that SYS$PUTMSG doesn't then try to display the message (unless you want it to.) See the description of $PUTMSG in the System Services Reference Manual for an example of using an action routine.

10.5 How do I link against SYS$SYSTEM:SYS.STB on an Alpha system?

LINK/SYSEXE is the OpenVMS Alpha equivalent of linking against SYS.STB. This links against the base image: SYS$BASE_IMAGE.EXE

Also see Section 10.11, particularly for pointers to the details on shareable images and shareable image creation.

10.6 How do I do a SET DEFAULT from inside a program?

The problem is that SYS$SETDDIR only changes the default directory - NOT the default disk. The default disk is determined by the logical SYS$DISK. If you want to change the default disk within a program, then call LIB$SET_LOGICAL to change the logical SYS$DISK. You will need to call both LIB$SET_LOGICAL and SYS$SETDDIR to change both default disk and the default directory!

10.7 How do I turn my Fortran COMMON into a shareable image on Alpha?

You need to add SYMBOL_VECTOR=(<common-name>=PSECT) to your options file. On OpenVMS VAX all OVR/REL/GBL psects were automatically exported into the shareable image's Global Symbol Table. On OpenVMS Alpha you have to tell the linker that you want this done by means of the PSECT keyword in the SYMBOL_VECTOR options file statement.

This has several advantages over OpenVMS VAX. First, you don't have to worry about the address of the psect when you try to create a new, upwardly compatible version of the shareable image. Second, you can control which psects, if any, are made visible outside the shareable image.

By default, COMMON PSECTs in HP Fortran for OpenVMS Alpha (as well as most other OpenVMS Alpha compilers) are NOSHR. On VAX, the default was SHR which required you to change the attribute to NOSHR if you wanted your COMMON to be in a shareable image but not write-shared by all processes on the system. If you do want write-sharing, use:

CDEC$ PSECT common-name=SHR 

in the Fortran source code (the CDEC$ must be begin in column 1) or a linker options file PSECT_ATTR statement to set the COMMON PSECT attribute to SHR.

For further information, see the Linker manual.

10.8 How do I convert between IEEE and VAX floating data?

In OpenVMS V6.1 and later, the routine CVT$CONVERT_FLOAT is documented in the LIB$ Run-Time Library Reference Manual, and can perform floating point conversions between any two of the following floating datatypes: VAX (F,D,G,H), little-endian IEEE (single, double, quad), big-endian IEEE (single, double, quad), CRAY and IBM System\370, etc.

HP Fortran (all OpenVMS platforms) has a feature which will perform automatic conversion of unformatted data during input or output. See the HP Fortran documentation for information on "non-native data in I/O" and the CONVERT= OPEN statement keyword.

There are floating-point conversion source code packages available for various platforms.

For further floating-point related information, see:

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