Compaq Contura 3/25C 80386 Laptop

4.00 avg. rating (84% score) - 1 vote

I recently picked up a free Compaq Contura 3/25c, a very old IBM-compatible laptop computer from the early 1990s, with a 25MHz 80386 processor, 4MB onboard memory and 3.5in 1.44MB floppy drive. The original 120MB hard drive has been removed by the previous owner. The laptop is also in very bad shape, with dust all over the place and the LCD panel removed:

The laptop must have looked like this when new with the 8.4 inch black and white LCD:

I was trying to make it boot up by connecting an external monitor to the VGA port when I noticed that the VGA port is actually keyed via pin #9. No modern VGA cable would fit into this port until you break pin #9 on the cable or punch a hole on pin #9 of the port. Since there is actually no need to key a VGA DB9 connector because the shape of the port would prevent you from inserting it upside down anyway, later VGA ports used pin #9 as an optional +5V DC source.

CMOS Battery

The unit boots up with a “RTC Lost Power” error message (see this for a full list of Compaq POST error messages). This is quite common with old laptop when the CMOS battery finally dies after a few years. So I opened it up in order to replace the battery:

The laptop is using a CR2430 lithium coin battery placed in a socket to facilitate replacement. There is even a warning, in various languages, telling you about danger of explosion if the battery is incorrectly replaced. This surprised me, since modern laptops would probably just have the battery soldered onboard. Some may feature a motherboard socket for the battery connector, but the actual connections to the battery are permanently soldered, which means some wire-cutting and soldering needs to be done if the battery ever needs to be replaced. This is a CMOS battery from a newer laptop:

I quickly ordered a pack of 5 CR2430 cells for a cheap price from eBay. Notice the funny English on the packaging. Whoever typed this probably had no ideas what it means:

BIOS Setup

With the CMOS battery replaced and a PS2 keyboard connected, I started the machine. Although many old laptops and PCs do not have an onboard BIOS and require the use of startup disks containing the BIOS utilities to change system settings, this machine has one, available in several languages, accessible via F10 at startup:

There are 2 startup disks for this laptop, formerly downloadable from Compaq website:

  • Disk 1: BIOS setup utility
  • Disk 2: Diagnostic utility

However, these downloads were removed when Compaq was merged with HP in 2003 and a lot of legacy support was gone. Although I eventually managed to find the disks with the help of, disk 1 comes with no COMMAND.COM and boots up to a DOS error “Bad or Missing Command Interpreter” error message. I fixed the error by putting MS-DOS 6.22 on it. The images for both disks as well as the original tool to create the disks (SP2054.exe) can be downloaded here. You will need WinImage to write the images to floppy disks.

Unlike the motherboard SETUP, the SETUP utility on the disks uses graphic mode and takes a long time to start up:

Installing the hard drive

Since the original hard disk has been removed, my next task is to install a 2.5inch IDE hard drive before the notebook can be used for anything useful. Keeping in mind that laptops of this generation only use CHS addressing and do not support hard drive more than 512MB due to the 1,024 cylinders limitation, I have chosen a 270MB IBM DHAA-2270 hard drive:

Still, installing the hard drive turns out to be no easy tasks as the BIOS only supports a limited number of hard drives types (which does not include my drive). There is also no support for auto detection or user-defined types:

Interestingly, types 65 and 66 are empty, indicating that they are custom types and can be configured by either re-programming the BIOS as suggested in this forum discussion, or by writing a tool that modifies the BIOS hard disk type table stored in memory and hope that the BIOS will recognize the changes. Either way, it’s a shoot in the dark as I could find no instructions on flashing this laptop’s BIOS, and there is also no documented address where I can hope to find the type table.

However, there is an easier way by using a drive overlay such as ANYDRIVE or EZ-Drive. The trick is to specify a hard disk type in BIOS where the number of cylinders, heads and sectors is smaller than the actual value so that the BIOS will not report an error on POST and accept the hard disk. Once then, boot from a floppy disks with ANYDRIVE to set up the disk overlay, which will overwrite BIOS Int 13h (which is used by DOS to query hard drive info) and respond with the correct disk geometry values. Run FDISK to setup the hard disk and you will be able to use the full capacity.

This will work with DOS and Windows 3.1 or older which relies on Int 13h to access the hard disk. Operating systems such as Linux and some disk utilities may query the hard disk directly, resulting in possible data loss with the overlay installed. In Windows 3.1, 32-bit disk access must be turned off, otherwise Windows may also query the hard disk directly, resulting in similar problems.

Transferring files using Norton Commander

With the overlay installed, all existing data on the disk is lost and some PCs may also fail to recognize the drive. Since I do not want to copy data and programs to the laptop using floppy disks, the only other way is to use a serial or parallel cable, with the help of Norton Commander 5.0 Link utility.

Note that you cannot simply use a male-to-male serial or parallel cable, but rather a null modem or a Laplink cable respectively. Since these cables are extremely over priced, I decided to go for soldering a null modem cable myself using the connectors available in my junkbox, and the pinout from here. With my other PCs running Norton Commander (NC) from within Windows 98 acting as Master, I am able to copy the data to this laptop (acting as Slave). At a maximum theoretical speed of 115200bps, made slower by the noise-sensitive cable disrupting the copy process resulting in several misleading errors “There is not enough room to copy…” from NC, it took half a day to copy DOS programs, games and Windows 3.1 to the laptop.

However, before I could think of some useful purposes for this laptop, it dies and fails to POST with no beeps and no display output. On every boot, the system simply hung after attempting to seek the floppy drive. There were perhaps several symptoms that the laptop was dying, for example the fact that I needed to press the POWER button multiple times (although the button itself is fine, as checked by a multimeter) to turn the laptop on and the wrong memory count of 21885KBytes extended memory in BIOS:

Since all basic troubleshooting does not seem to help and there are no user replaceable parts inside the motherboard, I eventually removed the hard disk and ran FDISK /MBR to remove the overlay, and toss the machine. Everything has its time, I guess.

UPDATE (Feb 2014)

A reader shared with me that he had a similar Compaq Contura laptop whose LCD had failed and displayed random patterns upon being turned on, although it still seemed to boot properly as the POST beep could be heard. After several debugging attempts, he finally managed to fix the issue and the laptop could boot to Windows 3.1 successfully. The LCD failure was due to a broken PCB trace resulting from an electrolytic capacitor leak (see the comments section of this article for further details).

The complete set of photos and videos demonstrating the disassembly, the failure mechanism of the LCD as well as several Windows 3.1 screens once the LCD has been fixed can be viewed here.

Thanks to Fabio for his sharing! I am sure this will help other people who are trying to keep their Contura laptops and other similar vintage computers alive.

4.00 avg. rating (84% score) - 1 vote


A tough developer who likes to work on just about anything, from software development to electronics, and share his knowledge with the rest of the world.

54 thoughts on “Compaq Contura 3/25C 80386 Laptop

  • October 30, 2023 at 11:49 pm

    Win95 does OK on a Contura 3/20 and presumably the two faster versions also if upgraded to the maximum 6MB RAM, as mine was back in the day. It’s a weird little thing, based on the i8292SX, an Intel 80386SX SoC that basically integrates everything but the 80387 (if you chose to install one) and the memory and modem (again if you chose to install one). Lots of complicated timing stuff to run all that out of a 40 pin QFP. That’s presumably why more RAM is helpful on this sort of machine. But, as a result, they’re incredibly poorly documented and difficult to fix. Best of luck to you all.

  • ToughDev
    November 1, 2023 at 11:45 pm

    Hi James,

    Thanks for sharing. Great to hear that Win95 works OK on the Contura 3/20 even with a 386SX. The 80387 will definitely help to improve the performance, although I must say that there is (almost) nothing you can do with Windows 95 that cannot be done with Windows 3.11 on the Contura. I’d love to browse Internet Explorer via dial-up on Windows 95 on the Contura, perhaps with the help with the 80387, if that’s even possible at all.

    In terms of documentation older chips tend to have better documentation. Despite its age you can still find complete tutorials for the 8088 everywhere on the Internet. Nowadays, outside of a few niche and incomplete websites, it is hard to find any useful tutorials on how to write an EFI application. :)

  • November 25, 2023 at 5:50 am

    No kidding. I actually think there’s a very probable performance bottleneck with the 80387 that would be incurred in most circumstances other than DOS text-based spreadsheets in a practical sense. There’s just no way that the timing hardware could really handle it in any environment that requires frequent display refreshes in graphics mode. The color Contura 3/25c doesn’t have a socket for the 80387 whereas the grayscale 3/20 and 3/25 do, presumably because driving a 16-color display is far simpler than a 256-color display in terms of the demands placed on the timing hardware of the i8292SX.

    Yes, you’re right, bootloaders are almost as esoteric today as this was in the ’90s ;-)

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