The OpenVMS Frequently Asked Questions (FAQ)

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2.17.2 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 I64, the memory page size is also variable, ranging from 4096 bytes (4 kilobytes) up to 256 megabytes (MB) and potentially up to 4 gigabytes (GB). As with OpenVMS Alpha, sys$getsyi and f$getsyi and the PAGE_SIZE itemcode can and should be used to determine the current system page size. In general, OpenVMS I64 will use a page size of 8 kilobytes, or larger.

On OpenVMS Alpha and on OpenVMS I64, a 512 byte area of memory--- equivalent in size to an OpenVMS VAX memory page---is often refered to as a "pagelet".

2.17.3 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 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 (as used by marketing and by storage vendors) and base two (OpenVMS and various other operating systems) 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 
Exabyte   (EB)  10**18 1000000000000000000   2**60 1152921504606846976 

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.

FAQ Notation

Within the OpenVMS FAQ, a thousand bits (either assuming base two or base ten, as determined by the context) is refered to as a kilobit, and is always represented by the appreviation Kb, while a thousand bytes is refered to as a kilobyte and is always abbreviated 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 OpenVMS operating system, a microfortnight is approximately one second.

Chapter 3

If you are searching for something here, please consider using the text-format FAQ.

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 2.6.) 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.

Information on the XPDF DECwindows PDF viewer for OpenVMS is available in Section 13.1, and XPDF kits are available on various Freeware distributions. An alternative on OpenVMS Alpha uses the Adobe Java PDF viewer, though this viewer is generally considered to be both slower and more resource-intensive when compared to the XPDF viewer.

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 web 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 Sewell
proGIS Software
Jeff Cameron
David Mathog's (quite 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. This information is available at the Deathrow cluster.
Undocumented Features
DECUS Deutschland
Arne Vajhøj
The OpenVMS Freeware contains various examples of undocumented features and interfaces
Comparisons of UNIX and Linux shell commands and DCL Commands
Comparisons of emacs and OpenVMS text editor commands
  Please see Table 3-2 for listings of introductory web sites and related materials.
An OpenVMS Programming FAQ
Tutorial information and tips for connecting OpenVMS systems to the Internet
Documentation and Specifications for DECnet Phase IV, DECnet task-to-task DCL examples, and a whole lot more.
HP OpenVMS Documentation
  Please see Table 3-2 for listings of documentation web sites and related materials.
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 5.17.
Catalogs and Pricing
HP Product QuickSpecs and product information
The HP Systems and Options Catalog (SOC) archive
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.
dtrwiz's Datatrieve website

3.3 How do I extract the contents of a HELP topic to a text file?

To extract all the text of a HELP topic (and its subtopics) to a text file for perusal with a text editor, printing out, etc., use the following command:

$ HELP/OUT=filename.txt help-topic [help-subtopic] 

If the help text you want is not in the standard help library (for example, it's help for a utility such as MAIL that has its own help library), add /LIBRARY=libname after the HELP verb. To see the names of help library files, do a directory of SYS$HELP:*.HLB.

3.4 Does OpenVMS Marketing have an e-mail address?

Yes - if you can't get the answers to marketing questions elsewhere, if you have comments or complaints about OpenVMS, send mail to openvms-info{atsign} This address is not a support channel, and is solely intended to provide informal method to communicate directly with members of OpenVMS Marketing.

3.5 Where can I learn about OpenVMS executive internals?

The OpenVMS Internals and Data Structure manual (IDSM) explains how the OpenVMS executive works. The book covers the operating system kernel: process management; memory management; the I/O subsystem; and the mechanisms that transfer control to, from, and among these. It gives an overview of a particular area of the system, followed by descriptions of the data structures related to that area and details of the code that implements the area.

The first edition of the OpenVMS Alpha internals book describes Version 1.5. Although there have been several releases of OpenVMS Alpha since Version 1.5 (V6.1, V6.2, V7.0, V7.1, etc) and many details in the book are no longer accurate, it continues to provide a strong conceptual description of OpenVMS internals.

This book has been split into five pieces, each to be updated separately. The first such volume, published in early 1997, was "OpenVMS Alpha Internals and Data Structures: Scheduling and Process Control," which covers the Version 7.0 implementation of true multithreading and the changed scheduling model it implies.

The internals books are available through Digital Press, see Section 3.6

3.6 Where can new users find tutorial information about OpenVMS?

First, see if your local site has information on this topic. Each site can have site-specific features and configuration. Some sites will have site-specific new user's documentation, covering various site-specific things that are difficult or impossible for the general OpenVMS documentation to cover.

3.6.1 Tutorial Websites?

Various websites with OpenVMS information are available; Table 3-2 contains some suggested URLs.

Table 3-2 OpenVMS Tutorial and Documentation Websites
URL Sponsor
  Various introductory materials
  Members of the Encompass DFWCUG maintain a website with many materials available, including an Overview of OpenVMS, an Introduction to DCL and the TPU Editor, Advanced DCL Command Procedures, OpenVMS Operations: Batch, Print, Tape, an Introduction to OpenVMS Management, to OpenVMS User Management, to OpenVMS Network Management, and to OpenVMS Cluster Management. These training materials have been presented at various DECUS symposia.
  A comparison table of various command-level tasks, with information on the UNIX and Linux shell command(s), and on the OpenVMS DCL command(s).
HP OpenVMS Documentation
  Various introductory guides as well as more advanced manuals are available in the OpenVMS and layered product documentation set.
HP OpenVMS Training
  HP offers training information and Technical Resource Kits (TRKs) and other Training for OpenVMS. An OpenVMS certification (testing) program is also available.
  An OpenVMS Quiz
  CCSS Interactive Learning has OpenVMS training materials
  AcerSoft Training information, and Shannon Knows Punditry
  MindIQ training information
  Quadratrix; OpenVMS training, products and services; affiliated with Global Knowledge and KeyJob

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