Follow-up: Unisys CWD 4001

November 11, 2017 dos cwd4001 hardware

I figured that I would post a follow-up regarding the Unisys CWD 4001 mini 486 PC I picked up earlier this year. I've had a few people now ask me various questions about it. It is certainly an interesting PC, especially for those looking for a nice compact retro PC to play around with so I certainly don't mind posting some more information about it to help out anyone else with questions regarding it.

Almost six months later and I'm actually not using mine that much, as I ended up building another 486 PC in a baby AT case. This was mainly because I wanted to be able to toy around with different hardware customizations, have more options for sound cards and have internal CD-ROM and 5.25" floppy drives. Otherwise my CWD 4001 is still working perfectly fine.

Hard Disk

As mentioned in my previous post earlier this year, the hard drive it originally came with died so I replaced it with a CF-to-IDE adapter. I got a StarTech IDE2CF and a Transcend CF200I 512 MB Compact Flash card. I had to cover the bottom of the adapter with electrical tape as otherwise some of the pins on the bottom would short against the metal part of the case it is resting on (and I could not find any kind of mounting bracket to fit in there instead).

The jumpers I have configured on the CF to IDE adapter set it for 3.3V power and master mode, drawing external power from the adapter you can see plugged in in the photo.

The BIOS configuration that I use for this is 987 cylinders, 16 heads, 63 sectors. If you end up using a CF card to replace a hard disk, make sure you do a FDISK /MBR or you may end up puzzled for a while like I was as to why you are mysteriously unable to boot from it!

You should be able to use a larger CF card if that's all you have (for a short while I was using an 8.4GB IDE hard disk without issue). Though with MS-DOS 6.22 you will only be able to use partitions with a max size of ~500MB.


Mine came with an AMD 486 DX2-66 already and that's what is still installed as I write this. However, these should work fine with up to a DX4 (some even had a DX4 pre-installed). On my CWD-4001 there is a voltage regulator on the motherboard so this should support 5V and 3.3V CPUs just fine, but I've not actually tried this. Do your own research first before trying!

On the underside of the motherboard on my CWD 4001 there is a motherboard diagram showing jumper settings. I've heard some people didn't have this, so I'll share what mine looks like:

The CWD 4001 doesn't include any L2 cache but since these are 486 machines, I believe all CPUs that these would ever have shipped with had 8KB L1 cache. The BIOS has an option to enable CPU write-back cache so if you have, for example, an Intel 80486 SX955 (P24D) then you can make full use of it. Though you will also have to configure the jumpers as shown in the diagram above. However, probably most people won't have a CPU with write-back cache support. Not to worry if you don't, it doesn't make a massive (real world) performance difference anyway.


For MS-DOS, you'll want the NE2000 packet driver. Then you'll want to add this to your AUTOEXEC.BAT with something like the following:

C:\NET\NE2000.COM 0x60 10

Where the 10 is the IRQ for the network adapter. Mine was set to 10, yours might not be (IRQ 10 or 11 were very commonly used for network adapters). I didn't have to tinker with any BIOS settings to make this work (not that there really is much of anything that you could change that would affect this to be honest).


As mentioned in my previous post, I'm using a Creative Sound Blaster CT4170 (Vibra 16XV). Your options for sound cards are quite limited with a CWD 4001 due to the compact size of the case. As far as Creative cards go, you'll probably be stuck to only a few of the later models that were more compact. Probably the best choice is one of the AWE64 value cards that is more compact but I don't own this card personally. I'm unfamiliar with what other Sound Blaster clone cards may fit.

For me, using IRQ 5 and 7 both worked. Remember that IRQ 7 is also used for the parallel port (LPT1), so if you're using any parallel port device you may want to configure your sound card to use IRQ 5 instead.

I have the following in my AUTOEXEC.BAT for my CT4170:

SET BLASTER=A220 I5 D1 H1 P330 T6


The CWD 4001 I would say is pretty average for a 486 DX2-66 system. It does not have VLB graphics, but the Cirrus Logic GD5424 isn't too bad really. The lack of L2 cache is also unfortunate, but the RAM speed seems a bit faster than other 486 systems I've tried... maybe something specific to the chipset/motherboard? Not sure really. The two RAM sticks installed in my CWD 4001 are nothing special, two HYM532220W-70 (72-pin 8MB 70ns) sticks.

Versus the other 486 system I built (Intel 80486 SX911 CPU, FIC 486-PVT motherboard, S3 Trio32 VLB, 16MB RAM) just for a slightly apples-to-oranges comparison:

How does this translate to "real world" performance? Well, I can share with you the results from running Phil's DOS Benchmark Pack on both of these systems:

CWD 4001 FIC 486-PVT, SX911, S3 Trio32 VLB
3DBench 1.0 41.6 fps 50.0 fps
3DBench 1.0c 40.4 fps 48.2 fps
Chris's 3D Benchmark 26.9 fps 31.4 fps
Chris's 3D SVGA Benchmark 9.1 fps
PC Player Benchmark 10.1 fps 9.6 fps
PC Player Benchmark (640x480) 4.0 fps 3.8 fps
Doom (min. details) 71.4 fps 70.0 fps
Doom (max. details) 24.3 fps 26.1 fps

Not really too surprising here when comparing ISA graphics to VLB graphics (in particular the S3 VLB graphics cards tended to be top-tier, performance wise).


A few people have asked questions after obtaining their own CWD 4001 (or 4002) after seeing that they were missing some internal components. In particular I've seen some people missing the ISA riser card and/or the bracket that fits onto the inside back of the case which the back plate of an ISA card would slide into when installing one. I'm unsure what people are doing for replacements for these and even if they are easy to come by, but for people's reference I've taken a bunch of photos of the ISA riser card and the ISA back plate bracket thingy.

Anyway, I hope the above helps anyone else looking for information about these Unisys CWD mini 486 computers. Feel free to email me though if you have any additional questions of course (my email address is on the "About" page linked on the left).

Mini 486 PC: Unisys CWD 4001

June 30, 2017 dos cwd4001 hardware

UPDATE: I posted a follow-up here where I go into to more details about this PC which may be of some interest to you.

A couple weeks ago or so, I came across a forum post with someone showing off a mini 486 PC by Unisys. After a bit of searching, I discovered that there was a seller on eBay who had a bunch of these for sale so I would easily be able to get one. When I saw this, I instantly thought to myself "I must get one of those!"
EDIT: It seems a video someone posted about these got a bunch of people buying them from this eBay auction which in turn caused the seller to bump up the price considerably. I only paid $97 CAN for mine!

However, I decided to sleep on it and wait a few days first and see if afterwards I still wanted it. I had originally decided that I did probably want to either buy or build a 486 PC at some point -- actually scratch that. While I had initially thought it would be cool to go as far back as a 486, when I thought about it some more I realized that getting at least a Pentium would probably make more sense. This was because in addition to wanting to use it for some "old school" development purposes, I'd also definitely want to use it to play games. And a 486 wouldn't cut it for that use for me personally. And with this thought in my mind, the question of what exact hardware specs I should go for was left unanswered and I realized that I had to do more thinking on it all. And regardless, I wasn't in any rush as I was still having fun fiddling with Amiga-related things.

Well, after a couple days passed by I still found myself thinking about it quite a lot. Space is at a bit of a premium for me as lately I keep buying random electronics toys that I don't really need. But what other small 486 PCs am I likely to find or be able to build myself anyway? Plus it wasn't that expensive (well, shipping to Toronto cost more than the PC itself, but even so, I can afford it ... meh). So I bought one!

It arrived pretty quick (4 days). And my god, it is small!

There's little information out there about these that I was able to find, just a few web pages with spec lists and some French videos on Youtube from some guy doing both an overview and a tear-down. Evidently, the exact hardware that these come with can vary a bit, but mine was:

  • Model: Unisys CWD 4001-ZE, Manufacture date: Sept 10, 1995.
  • CPU: Am486DX2-S 66MHz, socket 1 LIF PGA 169-pin with star-shaped heatsink.
  • RAM: 16MB. 2x HYM532220W-70 (72-pin 8MB 70ns DRAM).
  • Graphics: Cirrus Logic CL-GD5424, 1MB VRAM
  • Network: Accton/Unisys UK0022 (based on Novell NE2000)
  • Sound: PC speaker
  • Hard Disk: Fujitsu M1612TAU (545MB) IDE
  • Floppy Disk: Teac FD-05HG-4684-U (Slim)
  • Expansion: One unused ISA slot
  • Ports: 15-pin VGA, DB25 parallel port, 2x DB9 serial port, 2x PS/2 port (keyboard/mouse), RJ45 network port
  • PSU: Built in (proprietary).

Total dimensions: 29cm x 22cm x 6cm (width/depth/height).

Here's what the motherboard looks like for those curious (click for full picture):

In the above picture, the floppy drive, hard disk, and ISA riser have all been removed of course. But with them all in there it's packed in pretty tight! I was a little bit concerned about what the temperature might be like when it's been running for a while, especially since the only fan in the whole computer is a small one for the PSU only.

Honestly, I'm quite happy with these specs! I knew it was possible that these could come with anything from a 486DX2 33MHz to a 486DX4 100MHz, and I was hoping for at least a DX2 66MHz since it's what's largely regarded as a minimum spec necessary for playing games like Doom at a decent speed (you can do it with less of course, but then it all depends on your tolerance for lower framerates). 16MB of RAM is plenty and for a 486, you won't need any more at all. I was a little bit unfamiliar with the graphics cards of this era since I was younger at the time and had no money anyway, so I just used whatever was available to me (heh), but a GD5424 with 1MB VRAM is not too shabby either. Not amazing, just average really. Onboard LAN is quite nice, means I don't have to use floppy disks to transfer stuff to it since it's obviously lacking a CD-ROM drive.

Aside from the lack of a CD-ROM drive, the other big thing that is missing is sound. With no onboard sound capabilities aside from the lovely PC speaker and with a single ISA port available, getting a Sound Blaster card seemed like the obvious next step.

Of course, since this is such a small computer, one needs to take into account whether any given expansion card will actually fit into the case. Most of the better Sound Blaster card options are unfortunately too long.

I eventually settled on two possible options: a Sound Blaster AWE64 or a Sound Blaster Vibra 16XV. The few people I could find that had these computers all seemed to go with the AWE64 (something like a CT4520 is small enough to fit). I ended up going with a Vibra 16XV CT4170 mainly because I found one locally for cheaper, but would've gone for an AWE64 otherwise myself.

The only other thing of note was that within a few days of having this computer, the Fujitsu hard disk it came with died. I didn't intend to use that disk over the long term and had already ordered a CF-to-IDE adapter to replace it with. However, since the adapter hasn't arrived yet, I ended up replacing the drive temporarily with an 8.4GB Maxtor drive I still had sitting around. The BIOS only recognizes 2GB and is only able to boot from a partition that is 504MB (max) however.

For the first several days I was using an old SyncMaster 943N 19" 4:3 LCD monitor but grew tired of the poor upscaling of low MS-DOS resolutions. Picked up a cheap CRT monitor (a 15" Sony Trinitron CPD-100SX) from someone on Kijiji and now I really feel like it's all come together as a real old-school DOS PC!

In the above picture, the text editor on-screen is RHIDE for use with DJGPP. I was fiddling with some VGA Mode 13h C code... a nice trip down memory lane.

Overall, I'm glad I got it. It runs great, it's quiet, for a 486 it's decently specced and runs pretty much any games I throw at it from up until about 1996 or so (then you start getting into games really intended for Pentiums). Even Duke Nukem 3D is playable at 320x200, though barely. I actually think that the CF-to-IDE hard disk would help here as I do notice the game does load stuff from disk during game play here and there, and it seems like those disk accesses usually correspond with a slow down.

After the computer has been running for a while, the PSU does heat up quite a bit and the case does get warm to touch on that side. It still does concern me a little and I might investigate to see if I can get a better fan. Also, I would hope that once I remove the "big" hard disk and replace it with a much smaller CF card that it might help improve airflow inside the case and possibly reduce the internal temperature a little bit. However, from what I can tell from the few other forum posts that I've found from others who own this computer, heat doesn't seem to be a problem. So, fingers crossed that it remains that way as I'm not sure what else I could do (nowhere inside the case that I could install an additional fan or anything like that).