The OpenVMS Frequently Asked Questions(FAQ)

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2.10 Are there any network-accessible OpenVMS systems?

Yes, though various restrictions can and do apply.

2.11 What version of OpenVMS do I need?

For information on supported platforms, please see the OpenVMS Software Product Description (SPD) for the particular OpenVMS version of interest.

For a table of OpenVMS versions for various platforms, please see:

For information on the Multia, related Alpha single-board computers, or other officially unsupported systems, please see Section 14.4.1 and Section

The following is a rule-of-thumb for Alpha platform support. The table Table 2-4 contains the earliest OpenVMS Alpha release with support for a particular series of Alpha microprocessors:

Table 2-4 OpenVMS Alpha Version Rule-Of-Thumb
Microprocessor Generation OpenVMS Version General Comments
21064 EV4 V1.0 few systems; most EV4 require later; upgrade available
21164 EV5 V6.2 subsequent upgrade available
21164A EV56 V6.2-1H3 subsequent upgrade to V7.1 and later
21264 EV6 V7.1-2 subsequent upgrade typically to V7.2-1 or later
21264A EV67 V7.1-2 subsequent upgrade typically to V7.2-1 or later
xxxxxx EV68 V7.2-1 believed/probable; currently expectation

2.12 How can I submit OpenVMS Freeware?

For the guidelines and submission info, please visit the URL:

To order the current OpenVMS Freeware CD-ROM kit (shipping and handling charges apply), please request part number QA-6KZAA-H8.

2.13 Porting applications to OpenVMS?

Porting can range from simple to rather complex, and depends on the features used on the original platform.

This section covers generic porting, and porting from OpenVMS VAX to OpenVMS Alpha. (Porting from OpenVMS VAX to OpenVMS Alpha is often quite simple and involves little more than rebuilding from source, though a few applications using features specific to VAX will require some additional effort to port.)

Several manuals on porting from OpenVMS VAX to OpenVMS Alpha are available in the OpenVMS documentation set, including information on porting VAX Macro32 assembler code to the Macro32 compiler on OpenVMS Alpha, on management differences, on upgrading privileged code, and application migration:

Details on the C programming environment are available at:

Details on porting VAX C to HP C are are available at:

An OpenVMS Porting Library is available at:

Information on the Enterprise Toolkit, a Visual-based development environment for developing applications for OpenVMS using a Microsoft platform, is available at:

Details on DCE, CORBA, BridgeWorks, and COM/DCOM middleware is available at:

Information on the COE standards is available at:

A wide variety of programming development tools and middleware are available as commercial products (eg: DECset, IBM WebSphere MQ---formerly MQseries), and various tools are also available as shareware or as Freeware. Please see other sections of this FAQ, and please see:

2.14 What resources are available to OpenVMS software developers?

The HP Developer and Software Product Partner (DSPP) program is open to and intended to support and to assist HP OpenVMS software partners, consultants, and service providers:

DSPP provides members with various benefits, please see the website for details.

For those not familiar with the DSPP program or with its history, the DIGITAL Association of Software and Application Partners (ASAP) program and the DIGITAL Independent Software Vendors Network (ISVN) program were incorporated into the Compaq CSA program, and the CSA program has subsequently been incorporated into the HP DSPP program.

Please see Section 2.7.3 for additional details on the DSPP program.

2.15 memory management, resource management, process scheduling, etc?

So you have been instructed to write a school research paper on OpenVMS, and you need technical content on the OpenVMS Virtual Memory System, on any memory segmentation, on OpenVMS Resource Management, on the OpenVMS File System, on the OpenVMS user interface, etc.

Invariably, your professor/instructor/teacher will ask you a series of questions. Most commonly, the questions will request descriptions of one or more of the following items, and at varying levels of detail:

Any particular presentation or research paper, and particularly a scholastic presentation, can have many different potential target audiences, and very different presentation levels. Further, the usual underlying reason for scholastic presentations and scholastic research projects really has little to do with the subject matter, it is a task specifically intended to teach the student(s) (eg: you) how to perform the research. The instructor already knows most of (all of?) the information that you have been asked to collect.

For very technical details on OpenVMS and OpenVMS internals, the book you want is the Internals and Data Structures Manual (IDSM), available in your school or computing center library, and the IDSM can also be purchased. Additional technical details of the Alpha microprocessor are available in the Alpha Architecture Reference Manual documentation that is available for download. (Pointers to Alpha technical documentation are available in Section 14.6, and elsewhere.)

For higher-level (less technical) details, the OpenVMS documentation set is available on-line. The Programming Concepts and the File Systems manual are probably the best manuals to start with, depending on the particular level of detail the research requires.

And please understand the hesitation of various folks to provide you with a completely-written research report on your topic. Why? We might have to work with you after you graduate---you need to know how to perform at least basic research on your own, regardless of the topic.

2.16 Basic Units of Measurement?

OpenVMS and the underlying hardware use various units of measurement for disk and memory storage, and related abbreviations also typically exist. This section covers the most common units, and the associated abbreviations.

2.16.1 How many bytes are in a disk block?

A disk block is the minimum unit of disk storage allocation in OpenVMS.

Under OpenVMS VAX and OpenVMS Alpha, the disk volume block size is consistent, with each block containing 512 bytes.

The minimum disk allocation granularity actually permissible (in the ODS-2 and ODS-5 volume structures commonly used on OpenVMS) is determined on a per-volume basis, and is typically based on a combination of the total number blocks on the disk volume and the total size of the volume storage bitmap. The allocation granularity is known as the volume cluster factor---the cluster factor is the number of blocks in a disk cluster, and it is the smallest number of blocks that can be allocated on a particular disk volume.

Prior to OpenVMS V7.2, the maximum permissible size of the bitmap requires larger cluster factors as volume sizes increase. Starting with V7.2, the bitmap can be larger, and cluster factors as small as one block can be used.

The number of bytes in a file can be determined by multiplying the number of blocks allocated for the file times the number of bytes in a block. For sequential files (only), the FFB (XAB$W_FFB, in the File Header XAB) value can be used to find out how much of the last (XAB$L_EBK) block is used. FFB and EBK are meaningful only for sequential files, and only in a limited context---partial block allocations are not permitted. For other file formats, the EOF marker is not meaningful.

Disk allocations always occur only in units of the cluster factors, which can be from one block up to (potentially) clusters of eighteen blocks or more, depending on the volume cluster factor. (OpenVMS V7.2 and later optionally provide for a cluster factor of one up to volumes of approximately 137 gigabytes.)

OpenVMS assumes that the device driver and the underlying storage device will present the file system with addressable units of storage of 512 bytes in size, or the appearance of same. Various third-party CD-ROM devices, for instance, support only 2048 byte blocks, and such devices are incompatible with the standard OpenVMS device drivers.

To determine the number of bytes required for a file from DCL, one option uses the f$file_attributes item EOF, multiplied by the size of a block in bytes (512). This does not account for the unused space in the last block of a sequential file, but it also does not have to differentiate sequential files from other files.

2.16.2 How many bytes are in a memory page?

A memory page is the minimum unit of memory allocation in OpenVMS. With OpenVMS VAX, the memory page size matches the disk block size: it is always 512 bytes.

With OpenVMS Alpha, the memory page size is variable, and it can range from 8192 bytes (8 kilobytes) up to 64 kilobytes. The current system page size can be determined using the sys$getsyi or f$getsyi PAGE_SIZE item. Programs with hardcoded constants for the memory page size (or page alignment) should always assume a page size of 64 kilobytes.

On OpenVMS Alpha, a 512 byte area of memory---equivilent in size to an OpenVMS VAX memory page---is refered to as a pagelet.

2.16.3 How do I convert? Disk Blocks? KB, MB, GB, TB?

The smallest granularity of disk storage addressing is called a disk block, or sometimes a disk sector. Groups of disk blocks are usually organized together into the smallest unit of storage that can be allocated, and this unit is called a disk cluster. The number of blocks in a cluster is the cluster factor, and is established when the disk volume is initialized.

Each individual disk block is composed of five hundred twelve (512) bytes, or one-half kilobyte. Each byte is comprised of eight bits. A bit represents the smallest unit of information, typically refered to as a one or a zero.

OpenVMS tends to uses base two notation for disk storage, while disk storage capacity specifications from most storage vendors (including Compaq) will generally use base ten notation.

An OpenVMS disk block is 512 bytes in size; this is one-half kilobyte in base two notation.

The following table describes the prefix, the abbreviation, and the associated base ten (marketing) and base two (OpenVMS) values.

            Base Ten                        Base Two 
            -----------------------------   ---------------------- 
  Kilobyte  (KB)  10**3              1000   2**10             1024 
  Megabyte  (MB)  10**6           1000000   2**20          1048576 
  Gigabyte  (GB)  10**9        1000000000   2**30       1073741824 
  Terabyte  (TB)  10**12    1000000000000   2**40    1099511627776 
  Petabyte  (PB)  10**15 1000000000000000   2**50 1125899906842624 

The base ten representation of the 2**40 value is 1099511627776, which is obviously rather ugly. When viewed as a base eight or base sixteen (octal or hexadecimal, respectively) value, the value is far nicer. Specifically, the value is 10000000000 and 40000000 when represented in octal and hexadecimal, respectively.

Notational note: Within the OpenVMS FAQ, a thousand bits (either assuming base two or base ten, as determined by the context) is refered to as kilobit, and is always represented by the appreviation Kb, while a Kilobyte is always represented as KB. Similar notational usage also holds for Megabits (Mb) and Megabytes (MB), and for the various other units.

OpenVMS operating system references to system and storage are generally to the base-two version (eg: 1024, in the case of a kilobyte or kilobit) while storage hardware references and hardware specifications are generally to the base-ten version (eg: 1000).

To convert OpenVMS disk blocks to (base two) kilobytes (KB; 1024 bytes), simply divide by two. To convert blocks to (base two) megabytes, divide by 2048. Blocks to (base two) gigabytes (GB), divide by 2097152. These particular divisions can also be performed using bitshifts: to divide a value by two, shift the binary value rightward by one bit position.

To convert OpenVMS disk blocks to (base ten) kilobytes, divide by approximately 1.953125.

For those folks with an interest in odd applications for prefixes, and particularly for those folks also rummaging around deep within the system parameter listings, a microfortnight is approximately one second.

Chapter 3

3.1 Where can I find online copies of OpenVMS manuals?

The HP OpenVMS and HP Layered Product documentation is copyrighted material.

HTML format on-line product documentation sets for specific HP OpenVMS products are presently available at:

Documentation is offered on separately orderable CD-ROM media through a subscription to the Consolidated On-Line Documentation (ConOLD) product (see Section 2.5.) ConOLD manuals are readable with BNU, a viewer that is supplied with the documentation distribution. BNU can display HTML, Bookreader, and documentation in other formats.

MGBOOK, a viewer for Bookreader-format documentation is available for character-cell terminals (eg. VTxxx) via the WKU VMS Freeware file server -- see question Section 13.1 for details.

3.2 What online information and websites are available?

On your OpenVMS system, the HELP command can provide a wealth of information, not only on DCL commands but on system services (HELP System_Services) and Run-Time Library routines (HELP RTL_Routines). The introduction displayed when you type the HELP command with no additional keywords provides further pointers.

OpenVMS Marketing runs a WWW server at Here, you will find product information, strategy documents, product roadmaps, the contents of the latest OpenVMS Freeware CD-ROM and more.

Table 3-1 OpenVMS Websites
URL Sponsor
  HP OpenVMS Marketing
  Encompass DFWCUG
  Arne Vajhøj
  Saiga Systems
  Wayne Sewel
  Sponsored by proGIS Software
  Jeff Cameron
  David Mathog's (useful) information about OpenVMS.
  "The Beave"
Includes system cracking information that can be of interest to OpenVMS System Managers, and to OpenVMS Network and Security Managers.
Undocumented Features
  DECUS Deutchland
  Arne Vajhøj
  The OpenVMS Freeware contains various examples of undocumented features and interfaces
  An OpenVMS Programming FAQ
  Tutorial information and tips for connecting OpenVMS systems to the Internet
  Documentation and Specifications for DECnet Phase IV
HP OpenVMS Documentation
  Various introductory guides as well as more advanced manuals are available in the OpenVMS and layered product documentation set.
  Software Product Descriptions (SPDs) for most every OpenVMS-related product HP sells.
System Performance
  See Section 14.2.
Patch (ECO) Kits
  For the HP Services FTP server hosting Various contract-access and non-contract access ECO (patch) kits, see section Section 5.16.
Catalogs and Pricing
  HP Product QuickSpecs and product information
  The HP Systems and Options Catalog (SOC) archive
  Pointers to country-specific product information, pricing, and related. The services formerly provided by BusinessLink are being replaced by these and other country-specific mechanisms, please see the URL for details.
  The OpenVMS Times Newsletter
  The DFWCUG Quadwords Newsletter
  Back issues of the (discontinued) Digital Technical Journal (DTJ)
  The HP (Compaq) inFORM Magazine
Hardware and Software Archives
  The VAXarchive, including hardware and software information
  A VAX to Alpha upgrade diary
  Scanned versions of old DIGITAL manuals from DFWCUG
  A wide variety of HP VAX, Alpha, platform and other product documentation. Some introductory, some technical.

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