HP OpenVMS Systems Documentation

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The OpenVMS Frequently Asked Questions (FAQ)

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14.10 What is the layout of the VAX floating point format?

The VAX floating point format is derived from one of the PDP-11 FP formats, which helps explain its strange layout. There are four formats defined: F 32-bit single-precision, D and G 64-bit double-precision and H 128-bit quadruple precision. For all formats, the lowest addressed 16-bit "word" contains the sign and exponent (and for other than H, some of the most significant fraction bits). Each successive higher-addressed word contains the next 16 lesser-significant fraction bits. Bit 15 of the first word is the sign, 1 for negative, 0 for positive. Zero is represented by a biased exponent value of zero and a sign of zero; the fraction bits are ignored (but on Alpha, non-zero fraction bits in a zero value cause an error.) A value with biased exponent zero and sign bit 1 is a "reserved operand" - touching it causes an error - fraction bits are ignored. There are no minus zero, infinity, denormalized or NaN values.

For all formats, the fraction is normalized and the radix point assumed to be to the left of the MSB, hence the following range: 0.5 less than or equal to f and less than 1.0. The MSB, always being 1, is not stored. The binary exponent is stored with a bias varying with type in bits 14:n of the lowest-addressed word.

  FP      Exponent    Exponent    Mantissa (Fraction) bits,
  Type      Bits        Bias        including hidden bit
   F         8           128              24
   D         8           128              56
   G        11          1024              53
   H        15         16384             113

The layout for D is identical to that for F except for 32 additional fraction bits.

Example: +1.5 in F float is hex 000040C0 (fraction of .11[base 2], biased exponent of 129)

14.11 Where can I find more info about VAX systems?

14.12 Where can I find information on NetBSD for VAX systems?

Gunnar Helliesen maintains a NetBSD VAX FAQ at

14.13 What system disk size limit on the MicroVAX and VAXstation 3100?

System disks larger than 1.073 gigabytes (GB)---1fffff hexidecimal blocks -- are not supported on any member of the VAXstation 3100 series and on certain older members of the MicroVAX 3100 series, and are not reliable on these affected systems. (See below to identify the affected systems---the more recent members of the MicroVAX 3100 series systems are NOT affected.)

Various of the SCSI commands used by the boot drivers imbedded in the console PROM on all members of the VAXstation 3100 series use "Group 0" commands, which allow a 21 bit block number field, which allows access to the first 1fffff hexidecimal blocks of a disk. Any disk references past 1fffff will wrap---this wrapping behaviour can be of particular interest when writing a system crashdump file, as this can potentially lead to system disk corruptions should any part of the crashdump file be located beyond 1.073 GB.

More recent systems and console PROMs use "Group 1" SCSI commands, which allow a 32 bit block number field.

There was a similar limitation among the oldest of the MicroVAX 3100 series, but a console boot PROM was phased into production and was made available for field retrofits---this PROM upgrade allows the use of the "Group 1" SCSI commands, and thus larger system disks. There was no similar PROM upgrade for the VAXstation 3100 series.

Systems that are affected by this limit:

  • VAXstation 3100 series, all members. No PROM upgrade is available.
  • MicroVAX 3100 models 10 and 20. No PROM upgrade is available.
  • MicroVAX 3100 models 10e and 20e. Only systems with console VMB versions prior to V6.4 are affected. A PROM upgrade for these specific systems is (or was once) available.

Also see

Also see Section 9.5.

14.14 What are the VAX processor (CPU) codes?

   CPU:    Platform:
   -----   ---------
   KA41-A : MicroVAX 3100 Model 10 and 20
   KA41-B : VAXserver 3100 Model 10 and 20
   KA41-C : InfoServer
   KA41-D : MicroVAX 3100 Model 10e and 20e
   KA41-E : VAXserver 3100 Model 10e and 20e
   KA42-A : VAXstation 3100 Model 30 and 40
   KA42-B : VAXstation 3100 Model 38 and 48
   KA43-A : VAXstation 3100 Model 76
   KA45   : MicroVAX 3100 Model 30 and 40
   KA46   : VAXstation 4000 Model 60
   KA47   : MicroVAX 3100 Model 80
   KA48   : VAXstation 4000 VLC
   KA49-A : VAXstation 4000 Model 90/90A
   KA49-B : VAXstation 4000 Model 95
   KA49-C : VAXstation 4000 Model 96
   KA50   : MicroVAX 3100 Model 90
   KA51   : MicroVAX 3100 Model 95
   KA52   : VAX 4000 Model 100
   KA53   : VAX 4000 Model 105
   KA54   : VAX 4000 Model 106
   KA55   : MicroVAX 3100 Model 85
   KA56   : MicroVAX 3100 Model 96
   KA57   : VAX 4000 Model 108
   KA58   : MicroVAX 3100 Model 88
   KA59   : MicroVAX 3100 Model 98
   KA85   : VAX 8500
   KA86   : VAX 8600
   KA88   : VAX 8800
   KA600  : VAX 4000-50 (aka VAXbrick)
   KA610  : MicroVAX I, VAXstation I (aka KD32)
   KA620  : rtVAX (VAXeln)
   KA62A  : VAX 6000-200
   KA62B  : VAX 6000-300
   KA630  : MicroVAX II, VAXstation II
   KA640  : MicroVAX 3300, MicroVAX 3400
   KA650  : VAXstation 3200, MicroVAX 3500, MicroVAX 3600, MicroVAX III
   KA64A  : VAX 6000-400
   KA655  : MicroVAX 3800, MicroVAX 3900, MicroVAX III+
   KA65A  : VAX 6000-500
   KA660  : VAX 4000-200, VAX 4 upgrade
   KA66A  : VAX 6000-600
   KA670  : VAX 4000-300
   KA675  : VAX 4000-400
   KA680  : VAX 4000-500
   KA681  : VAX 4000-500A
   KA690  : VAX 4000-600
   KA691  : VAX 4000-605A
   KA692  : VAX 4000-700A
   KA693  : VAX 4000-605A
   KA694  : VAX 4000-705A
   KA730  : VAX-11/730
   KA750  : VAX-11/750
   KA780  : VAX-11/780, VAX-11/782
   KA785  : VAX-11/785
   KA7AA  : VAX 7000-600
   KA7AB  : VAX 7000-700
   KA7AC  : VAX 7000-800
   KA800  : VAXrta
   KA820  : VAX 8200, VAX 8300
   KA825  : VAX 8250, VAX 8350
   KA865  : VAX 8650

14.15 Where can I get software and hardware support information?

Please contact the HP Customer Support Center. Services and information, manuals, guides, downloads, and various other information is available via the support link at:

Various hardware and system documentation is available at:

TSM (Terminal Server Manager), DEChub, DECserver, etc. information:

The owner and maintainer of current DECserver and related hardware is DIGITAL Network Products Group (DNPG):

14.16 Where can I get hardware self-maintenance support assistance?

The HP Parts Directory and the HP Parts Reference Guide (arguably the most direct descendents of the HP Assisted Services program, of the Compaq Assisted Services program, and of the now-ancient DECmailer program) are available to customers that wish to maintain their own system(s) (self-maintenance), but that wish some level of assistance in acquiring specific parts, hardware diagnostics and hardware manuals for the system(s), and that wish to have access to spares and module-level repairs for customer-performed hardware module swaps:

The HP Parts Reference Guide replaces the CAS-Catalog and DAS-Catalog parts catalogs and related resources.

Details of the available self-maintenance programs and services can vary by geography and by the particular services channel(s), and current program specifics are available via the above URLs.

14.17 Why does my system halt when I power-cycle the console terminal?

Various VAX and Alpha consoles are designed to process the BREAK signal, treating it as a HALT request.

A BREAK is a deliberately-generated serial line framing error.

When a serial line device such as a terminal powers up (or sometimes when powering down) it can generate framing errors. These framing errors are indistingushable from a BREAK signal.

When a BREAK is received on a serial line console for various VAX systems---including most VAXstation, MicroVAX, and VAX 4000 series---it is typically interpreted as a HALT. Alpha systems will also often process a BREAK in a similar fashion, halting the system.

There is no uniform or generally-available way to disable this behaviour on every VAX or Alpha system. On some systems, BREAK processing can be disabled in favor of [CTRL/P], or [CTRL/P] is the only way to halt the processor.

The most common way to avoid these halts is to disable the serial line console or to simply not power-cycle the console terminal. There is certain important system state information that is displayed only on the console, OpenVMS expects to always have access to the system console.

Also see Section 5.6.

14.18 Can I reuse old keyboards, mice and monitors with a PC?

Older HP keyboards (those with the DIGITAL logo and the RJ modular jacks), older HP mice (those with the DIGITAL logo and with the RJ modular jacks, or with a DIN connector with pins in a configuration other than the PC-standard DIN connector pin orientation), and older video monitors (with RGB synch-on-green video signaling) all use signaling formats and/or communications protocols that differ from the PC standards, and are not (easily) interchangable nor (easily) compatible with typical PC peripheral device controllers. The LK201 and LK401 keyboards, the VSXXX series mice, the VR260 and VR290 monitors, etc., are incompatible with most PC systems and with most KVM switches.

Newer HP (and Compaq) keyboards (those with with PC-style DIN plugs, and the HP, Compaq or DIGITAL logo), newer HP mice (with PC-pin DIN plugs, and the HP, Compaq or DIGITAL logo), and newer video monitors (multi-synch) are often interchangeable with "industry standard" PC systems, and can often be used with most PC peripheral device controllers. LK461, LK463, LK46W, LK471, PC7XS-CA, VRC16, VRC21, TFT-series LCD flat-panel displays, etc., are typically reasonably compatible with most PC systems, and will usually perform as expected within the limits of the hardware. (For details of CRT and LCD display compatibility, please see Section 14.19.)

Rule of thumb: if the peripheral device component was sold for use with the DEC 2000 (DECpc 150 AXP), an AlphaServer series, an AlphaStation series, or a more recent Alpha system, it will probably work with a PC peripheral controller or with a PC-compatible KVM switch. If the peripheral device component was sold for use with an VT420 or older terminal, most VAX, most VAXstation, and most Alpha systems with names in the format DEC [four-digit-number], it probably won't work on a PC system or with a PC-compatible KVM.

Note that the above is a general guideline, and should not be read to indicate that any particular peripheral device will or will not work in any particular configuration, save for those specific configurations the device is explicitly supported in.

Software Integrators sells a video adapter card called Gemini P1 which will drive many of the older HP (DIGITAL-logo) fixed-frequency monitors on a PC system:

The DIGITAL (classic 2-5-2-style) part number 29-32549-01 converts the output from the RGB cable (3 BNC, synch-on-green) that comes with the VAXstation 3100 and VAXstation 4000 series to a female SVGA D connector. You may be able to find third-party converters or adapters (3 BNCs with synch-on-green signaling to 5 BNCs with VGA/SVGA, or to 15-pin VGA/SVGA.

This adapter will allow PC multisync monitors with the needed frequency specifications to be used with the VAXstation series synch-on-green video connection. It may well also work with a VAXstation 2000 series systems, but specifics and performance of that combination are not immediately known at this writing.

The protocol definition for the old DIGITAL keyboard and mouse interfaces is buried at the back of the QDSS section in the old VAXstation II manual, specifically, in the back of the VCB02 Video Subsystem Technical Manual (EK-104AA-TM). The keyboard wiring and protocol is in appendix B, and occupies circa 44 pages. The mouse is in appendix C, circa 12 pages.

Also see Section 14.19.

14.19 Which video monitor works with which graphics controller?

To determine the answer to the "will this video monitor or this LCD panel work with this graphics controller?" question, please first locate the resolution(s) and the frequencies that are possible/supported at both ends of the video cable (on the display and on the graphics controller, in other words), and then determine if there are any matching settings available. If there are multiple matches, you will need to determine which one is most appropriate for your needs.

You will also need to determine if the video monitor or graphics controller requires the 3 BNC signaling with the synchronization signals on the green wire, or the 5 BNC signaling common on many PCs, or other connections such as the DB15 video connector or USB connector used on various systems. (BNC signaling is comparatively old, but prevalent with many older hobbyist AlphaStation or VAXstation configurations.)

If there are no matches, you will likely need to change the hardware at one or both ends of the video cable.

The refresh frequencies for many devices have been posted to comp.os.vms and/or other newsgroups. Search the archives for details. Also see:

LCD-based and plasma-based flat-panel displays are generally compatible with all recent OpenVMS Alpha systems and supported graphics controllers. For best results, you should generally set the graphics controller to match the native LCD or plasma display resolution and (for LCD displays) also set the controller refresh rate to 60Hz. Check your graphics controller and your display documentation for any device-specific requirements and/or configuration recommendations.

Some of the older graphics controllers around do not necessarily generate stable signals at 60 Hz, if the controller can even generate that refresh rate; you may end up upgrading to a less-old controller. (At least some of the PowerStorm 3D30 and PowerStorm 4D20 series controllers, for instance, are not necessarily the best choice for 60 Hz operations with an LCD, based on empirical testing with an AlphaStation XP1000, PowerStorm 3D30, and a TFT2025 series LCD. Degraded or mismatched signals produce degraded displays, obviously. The newest graphics controllers compatible with your particular system are generally better choices here for use with LCD; the Radeon 7500 series is a good choice for most EV6-class AlphaStation systems, for instance.

Also see Section 14.18.

14.20 Where can I get information on storage hardware?

Information on various HP (Compaq, DIGITAL) OpenVMS and other disk storage hardware and controllers, and related technical information on SCSI, device jumpers, etc., is available at:


the aquascape website appears to have become unavailable, and the FAQ maintainer is unaware of a new or replacement server. You may or may not have some success looking for this or of any other now-unavailable sites using the world-wide web archives at:

14.21 Why does my LK401 keyboard unexpectedly autorepeat?

There are several modes of failure:

  • Pressing 2 and 3 keys at the same time causes one key to autorepeat when released. Check the hardware revision level printed on the bottom of the keyboard. If the revision level is C01, the keyboard firmware is broken. Call field service to replace the keyboard with any revision level other than C01.
  • Pressing certain keys is always broken. Typical symptoms are: delete always causes a autorepeat, return needs to be pressed twice, etc. This is frequently caused by having keys depressed while the keyboard is being initialized. Pressing ^F2 several times or unplugging and replugging the keyboard frequently fix this problem. (Ensure you have current ECO kits applied; there is a patch available to fix this problem.)
  • A key that was working spontaneously stops working correctly. This may be either of the two previous cases, or it may be bad console firmware. Ensure that you have the most recent firmware installed on your Alpha system. In particular, an old version of the DEC 3000 SRM firmware is known to have a bug that can cause this keyboard misbehaviour.

14.22 Problem - My LK411 sends the wrong keycodes or some keys are dead

Check the firmware revision on the keyboard. Hardware revision B01 introduced an incompatability with the device driver which causes the keyboard to not be recognized correctly. There is a patch available to fix this problem: [AXPDRIV06_061] - the fix is also included in OpenVMS V6.2. The rev A01 keyboard, and the LK450 should work without problems.

If you are working from another operating system platform, please see the DECxterm tool and related information on OpenVMS Freeware V5.0.

14.23 Which DE500 variant works with which OpenVMS version?

Ensure you have a version of the Alpha SRM console with support for the DE500 series device. Apply ALL mandatory ECO kits for the OpenVMS version in use, and also apply the CLUSIO, ALPBOOT, and ALPLAN kits, and apply any available ALPCPU ECO kit for the platform.

  • DE500-XA
    auto-detection, no auto-negotiation,
    OpenVMS V6.2-1H1 and ALPBOOT ECO, also V7.0 and later and ECO.
    Device hardware id 02000011 and 02000012.
    Component part number 54-24187-01
  • DE500-AA
    auto-detection, auto-negotiation,
    OpenVMS V6.2 and ALPBOOT and ALPLAN ECOs, or V7.1 and later and ECO.
    Device hardware id 02000020 and 20000022.
    Component part number 54-24502-01
  • DE500-BA
    auto-detection, auto-negotiation,
    OpenVMS V6.2-1H3 and CLUSIO, ALPBOOT, ALPLAN and ALPCPU ECOs, or V7.1-1H1 or later and ECO.
    Device hardware id 02000030 (check connector, vs DE500-FA) (other values on old Alpha SRM firmware)
    Component part number 54-24602-01
  • DE500-FA (100 megabit fibre optic Ethernet)
    OpenVMS V7.1-1H1 and later
    Device hardware id 02000030 (check connector, vs DE500-BA) (other values possible on old Alpha SRM firmware)
    Component part number 54-24899-01

To check the DE500 device hardware id from OpenVMS, use the following command:


The "hardware version" will be displayed.

To set the DE500 speed and duplex settings via the associated Alpha SRM console environment variable, see Table 14-4.

Table 14-4 DE500 Speed and Duplex Settings
EWx0_MODE setting Meaning
Twisted-Pair 10 Mbit/sec, nofull_duplex
Full Duplex, Twisted-Pair 10 Mbit/sec, full_duplex
AUI 10 Mbit/sec, nofull_duplex
BNC 10 Mbit/sec, nofull_duplex
Fast 100 Mbit/sec, nofull_duplex
FastFD (Full Duplex) 100 Mbit/sec, full_duplex
Auto-Negotiate Negotiation with remote device

To override the console setting and use LANCP:

LANCP> SET DEVICE EWA0/SPEED=100/full_duplex

Fast Ethernet (100Base, 100 megabit) controllers such as the DE500 series have a pair of connections available---while traditional Ethernet (10Base, 10 megabit) is inherently a half-duplex protocol, Fast Ethernet can be configured to use one or both of the available connections, depending on the controller. Fast Ethernet can thus be half- or full-duplex depending on the configuration and the capabilities of the network controller and the Ethernet network plant. Some Fast Ethernet controllers can also operate at traditional Ethernet speeds, these controllers are thus often refered to as 10/100 Ethernet controllers.

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