DEC UDB Information

In early 1996 I purchased a DEC Multia, a 233 MHz Alpha 21066 box with Windows NT. There was also an older 166 MHz model. They also offered the 166 MHz model with a bigger disk as an Easy Web Server.

DEC offered the 166 MHz model specifically for use with Linux (and without Windows NT) under the name UDB (Universal Desktop Box). The pricing was quite attractive.

The Multia, UDB, and Easy Web Server are no longer being sold by DEC (or Compaq). However, DEC dumped a large number of them at fire-sale prices, and there are still some distributors selling them.

Quick Index


The UDB only comes with a few sheets of drool-proof paper showing how to plug in the cables. More technical information is available in the 116-page manual "Multia MultiClient Desktop Service Information", DEC part number EK-MULTS-IN.C01. This manual is fairly pricey (about $85 in the US). Fortunately it is now available in machine-readable form:

udb-man.pdf, Adobe PDF format for Acrobat, 2.3 megabytes

Firmware Upgrade

DEC has made the firmware upgrade and failsafe loader disk images available on their FTP server. Be sure to read the readme.txt file for instructions.

If you are not having problems with your UDB, I don't recommend attempting to install the firmware upgrade. Most UDBs seem to have been shipped with the most recent firmware, and there appears to be very little difference between the old and the new firmware. Some people have reported problems installing the upgrade.

Memory Configuration

The UDB requires memory to be installed as pairs of "by 36" SIMMs, also known as "parity" SIMMs. It does not use EDO, and I'm not sure whether EDO SIMMs would even work. Note that "logic parity" SIMMs, which do not actually store 36 bits per word, will not work.

Some configurations of the VX41 and VX42 models are supplied with unusual 12 megabyte SIMMs. These SIMMs will only work in the first pair of SIMM sockets; if you try to use them in the other sockets, or in another system, they will only be recognized as 8 megabyte SIMMs.

The UDB doesn't actually use parity in the conventional sense. The 21066 microprocessor has a 64 bit data bus, with 8 additional bits for ECC (Error Correction Code). If you are running Linux, you may from time to time see ECC messages in the syslog, which look like this:

Nov  6 10:20:23 houhah kernel: lca: machine check (la=0xfffffc0000208490,pc=0x120011250)
Nov  6 10:20:23 houhah kernel:   Reason: correctable ECC error (short frame, retryable, dc_stat=0):
Nov  6 10:20:23 houhah kernel:     Correctable read error to b-cache occurred at address 56e9260

If these appear only rarely, they are not a cause for concern. It just means that the ECC is doing its job. On a system with only parity, instead of being corrected and logged, the error would cause a system halt. And on a system with neither parity nor ECC, the error would simply go undetected by the hardware. It could cause a crash, or it could cause some data corruption which might go unnoticed for a long time (especially if the data got written to disk).

If you get lots of ECC correctable error messages in the syslog, or if you get uncorrectable errors, you have cause for concern. This can be caused by defective SIMMs, mis-seated SIMMs, or a defective motherboard. The first thing to try is removing and re-seating the SIMMs. If that doesn't solve the problem, I would suggest trying a different set of SIMMs.

I believe that the following SIMMs sold by Crucial (Micron's retail business) should work, but I haven't tried them:

capacity Crucial part number
64 MB CT16M36P4M6
32 MB CT8M36P5M6
16 MB CT4M36P2M6
8 MB CT2M36P1M6
4 MB CT1M36P1M6

Note: On 11-FEB-2002, I received email from someone who purchased a pair of the Crucial 64 MB SIMMs listed above, and is successfully using them in his UDB.

Disk Configuration

The UDB was generally sold configured with either a 2.5 inch or a 3.5 inch internal SCSI disk. This was usually denoted by the last digit of the full part number of the unit. For example, a "VX42B-F2" has a 2.5 inch disk, while a "VX42B-F3" has a 3.5 inch disk.

Units incorporating a 3.5 inch disk have a different PCI riser card and mounting bracket. It is not possible to install a PCI expansion card in these units.

The UDB power supply is not capable of powering a second internal hard disk, and may not be sufficient to power even a single high performance drive, such as a Seagate Barracuda. I strongly recommend use of an external drive case.

If you do manage to install a 3.5 inch drive in a unit which originally had a 2.5 inch drive, you'll have to remove (or at least disconnect) the 2.5 inch drive.

As far as I know, there no 2.5 inch SCSI disk drives having storage capacities substantially exceeding 1 gigabyte. The UDB does have an internal IDE interface, with a 44-pin connector for both the IDE signals and power. This connector is commonly used with 2.5 inch IDE drives for portable computers. It is only a plain IDE interface, not EIDE, so it doesn't have any fast DMA or bus-mastering modes.

The necessary 44-pin IDE cable isn't very common, but I've been told that it can be purchased for $10 plus shipping as part number FC530 from Hard Data Ltd. I have not personally done business with them, but several other people who've emailed me have apparently been satisfied customers.

Jumper Settings

(166 MHz)
(166 MHz)
(233 MHz)
W9 W12 Mini console (auxiliary)
W8 (default) W10 Normal power-up sequence
W7 W11 Causes the system to attempt a floppy boot fail safe load (FSL)
W6 to W3 W6 to W3 Under SRM, these jumpers determine the resolution driven to the graphics display
W2 W2 When connected to a switch, causes a reset or halt (see J8)
J8 J8 When set 2 to 3 causes a reset, when set 1 to 2 causes a halt request CPU interrupt
none W9, W8, W7 CPU speed (see below)

CPU speed jumper settings (VX41/VX42 only)

W9 W8 W7 speed (MHz)
1 1 1 66
0 1 1 100
1 0 1 133
0 0 1 166
1 1 0 200
0 1 0 233
1 0 0 266 (unsupported)
0 0 0 300 (unsupported)

Note: 1 is jumper removed, 0 is jumper installed.

SRM Console video mode jumper settings

W6 W5 W4 W3 Standard Resolution Vertical Refresh (Hz) Pixel Clock (MHz)
0 0 0 0 VGA 640 x 480 59.94 25.175
0 0 0 1 ERGO VGA 640 x 480 72.79 31.50
0 0 1 0 SVGA 800 x 600 60.32 40.00
0 0 1 1 ERGO SVGA 800 x 600 72.19 50.00
0 1 0 0 VESA 1024x768 1024 x 768 70.07 75.00
0 1 0 1 Digital 1024x768 1024 x 768 72.033 74.367
0 1 1 0 Digital 1024x864 1024 x 864 60.00 70.00
0 1 1 1 1280x1024 60Hz (S3 86C928) 1280 x 1024 60.10 110.15
1 0 0 0 1280x1024 66Hz 1280 x 1024 66.51 119.843
1 0 0 1 1280x1024 72Hz 1280 x 1024 72.556 130.808
1 0 1 0 1280x1024 72Hz (S3 86C928) 1280 x 1024 72.05 130.08
1 0 1 1 1280x512 Stereo 1280 x 512 139.336 130.804

Note: 1 is jumper removed, 0 is jumper installed.

Serial Port Pinout

The UDB has two serial ports, but only one DB-25 connector. DEC sells an appropriate splitter cable (P/N BC25X-1F), but it is fairly expensive so if you are handy with a soldering iron or crimping tool you may wish to make your own.

COM1 is wired normally. COM2 is wired using the EIA-232E secondary channel pin assignments where they exist, and other pins (arbitrary?) for the rest.

Signal COM1 pin COM2 pin
TxD 2 14
RxD 3 16
RTS 4 19
CTS 5 13
DSR 6 23
signal ground 7
DCD 8 12
DTR 20 11
RI 22 25


I don't recommend overclocking, but many people report the 233 MHz system running fine at 266 MHz. Note that the early 166 MHz parts (21066-AA) were not capable of being run at these speeds; the faster parts resulted from a redesign in a smaller process. If you have a VX41 with a 166 MHz 21066-BB, you might be able to run it considerably faster.

Here are all the variants of the LCA that I have information on:

Chip Design Part Number Rated Speed Notes
21066-AA 166 MHz
21068-AA 100 MHz for embedded systems
21066-AB 233 MHz
21066-BB 166 MHz
21066-CB 100 MHz replaces 21068

Mitsubishi, a licensed second-source vendor, claimed to offer 200 MHz versions of the original 21066 (LCA4).

Linux Kernel Configuration

For UDB, the Linux Kernel should be configured as a NoName board. To make the sound system work, choose only the Microsoft Sound System support and the /dev/dsp and /dev/audio support. The settings should be:

I/O base 530

Performance Warning

Before you buy a UDB, be forewarned that the seemingly high clock rate does not mean that the machine is a screamer. For non-floating-point tasks, the 233 MHz model seems to offer performance comparable to a 100 to 120 MHz Pentium. However, the floating point performance is fairly good.

Reliability (or lack thereof)

Some people have reported great reliability, and others have had lots of problems. One of my VX42s works fine and the other has become flaky. Apparently there is a design flaw that causes one of the memory bus drivers to overheat; fortunately it is an inexpensive chip that can be replaced by a cooler-running CMOS version. The details are available from the NetBSD/alpha Multia Frequently Asked Questions page. Thanks very much to Tim Rightnour, author of the FAQ, for bringing this to my attention.

Other people have reported that replacing the fan helps.

Can I run OpenVMS?

DEC deliberately prevented the standard OpenVMS releases from working on the Multia, so as not to hurt their sales of big systems. However, if you get Compaq's Hobby License Agreement for OpenVMS (free for DECUS members, and basic membership is free), you can get the unsupported Multia foreign bootstrap kit, which apparently will make it work.

Where can I buy Multias and accessories?

Other Sources of UDB Information

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Last updated February 11, 2002

Copyright 1996, 1997, 1998, 1999, 2000, 2001, 2002 Eric Smith

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