DG One - jmp start ;microcomputers

Data General One

Posted on January 24, 2026January 25, 2026 by Graham

This machine came from Craig M of the ARC group. It is a Data General One from 1984. It is often credited as being the first battery powered IBM compatible(ish) laptop.

The impressively large LCD screen with its unimpressively low contrast is its Achilles heel. If not for that, it probably would have been a very successful machine.

The machine arrived with an expansion box, some disks, and lots of old-school manuals. Much of the software was packaged specifically for the One.

The Data General One Systems Programmer’s Manual contains a lot of technical detail about the machine include specific compatibility issues.

I also found this comprehensive and well-written article very helpful:

https://oldvcr.blogspot.com/2024/03/refurb-weekend-data-generalone-and.html

My story is different in that the machine came with a battery and an expansion unit, but did not come with a power supply. Somewhere along the way i also acquired the external 5.25″ drive unit but not the attachment cable.

Looking at the images in the article and comparing with my unit, i think the screen on mine seems to be somewhat clearer. It does seem to have what looks like some dust behind the panel, and it certainly needs good light (a camping headlamp works quite well) but it is quite useable if that’s all you have. It’s so much better, and clearly has a shade of green, that i wonder if the LCD is the same.

The expansion unit includes a floppy disk controller and 5.25″ floppy disk, a hard disk controller and a IMI hard disk built like a brick dunny, and a printer card. The manual indicated that it was possible for the system to use a CGA card in the expansion unit together with a CGA monitor to provide an external display – a blessed relief from the built-in LCD although far from portable.

The battery is charged from an external power pack, but it came as a surprise to learn that this was not intended to power the computer as well – although, as it transpired, it did do that job with some help from the battery. I couldn’t see this being sustainable.

Without an external supply or even the mating connector, i was forced to jump start it using a bench supply and some croc cables. Later i made up a power supply using an old laptop power supply and an adjustable DC/DC converter. The connector is a bit rough at present.

With power, the computer gave a beep and then, after a delay, it gave a further two beeps. The screen was blank initially but could be adjusted with the contrast buttons (command page-up and page-down). A carriage return allowed the system to boot from the front floppy drive.

Both symptoms were related to the backup battery being very flat. The battery was just a 2025 in a battery holder under the internal modem card.

The system reported a full 464kB of RAM – sadly, 48kB of the physical 512kB is lost to graphics memory. I have no idea whether another 128k can be added in the expansion unit.

I can confirm that the LCD screen is quite awful. It’s curious to me that Amstrad used a similar screen in its PPC512 a couple of years later. It was similarly awful, but at least external CGA was available on the Amstrad base machine.

The expansion unit connects to the computer via a cable and “dock”. The dock plugs into the expansion connector on the back of the computer and is held in place by two screws. When i tried to mount the dock, one of the mating nutserts released itself from the computer, and being worried that some debris may have been fallen inside the machine, i decided to open the unit. I had to anyway, to replace the battery.

Through this process, i learned that it is not necessary to remove the floppy disk drive screws or the keyboard screws.

The remainder do need to be removed, together with the 6 metal clips – three on each side. The LCD cable can be released via the battery compartment by pulling up on the top half of the connector. Then the top half of the computer can be lifted and completely removed if the power switch is disconnected.

You have to be impressed with the amount of electronics crammed into the unit. There is a lot of surface mount technology for 1984 and the line sizes on the PCBs are very small.

The top card in the stack is the internal modem card. This seems to be controlled through a parallel interface and seems only to be available to the ROM resident terminal program.

The next card is the I/O card with floppy disk controller, real time clock, and the two serial ports. There’s a ton of surface mount on the back, which i neglected to photograph. The offending 2025 real-time clock battery was replaced.

And that’s the main board with the 8088. Most of the cabling has been done with a flexible PCB which is very space efficient. I fear for its longevity, though, as the bends are quite severe.

The memory expansion unit is very cute with three 128MB cards.

After all that, there was no debris, and i cannot see any way to restore the nutsert. I did a full disassembly to clean the keyboard and to have a look at the innards.

Care has to be taken with the main board – the ground springs need to hook under the plastic insulating layer.

I was somewhat aghast to see some scratching on the main board. This is caused by a metal cable retaining clip under the DC/DC converter on the rear panel. I inspected this pretty thoroughly to make sure that no tracks had broken. I added some tape to the metal clip to protect the board. Not great design.

I have not resolved the issue with the dock mechanics, but i pressed on.

DG One Power Supply

Posted on January 24, 2026January 24, 2026 by Graham

The power arrangements for the machine are a little unusual. It can run from mains power adapter or from a large nicad battery pack. The battery pack is charged in the machine from a separate battery charger – not from the mains supply.

The mains supply, is according to ?????, a 30W 5.8V DC supply provided on a two pin connector of unknown type. I initially “jump started” the machine with a bench supply and some alligator clips.

The actual power drawn by the unit seemed to be no more than a couple of amps – perhaps the optional thermal printer takes power from the machine.

That seemed to be easily within the realms of a DC/DC converter. I found a simple one that could take a wide input voltage and could be adjusted to 5.8V. I’m yet to put it in a box, but it should be easy enough.

The DG One power connector is probably impossible to find but i did find some contacts that were close enough. I’ll need to craft a shell for the contacts.

As for the Nicad battery and charger – well, i think they can be relegated to exhibits.

DG One Expansion Unit

Posted on January 24, 2026February 1, 2026 by Graham

With the base machine seemingly working well, it was time to try my luck with the expansion unit. I really should have inspected the power supply first because it let out quite a lot of smoke from a line filter capacitor self emolliating.

Accessing it involved removing the cover, removing the fan cowling, and then releasing the supply which, conveniently, has connectors at both the mains and DC ends. I replaced both line filter caps.

The hard disk drive did spin up, but that seemed to be all it did. There didn’t seem to be any calibration activity. On power-down it sounded like it ground to a halt. I think it’s unlikely to be viable. I removed it – a very chunky full height IMI 18MB unit.

The floppy disk drive did work, which was good because that meant that the link to the expansion box was working and, of course, the floppy disk controller was also working. The 5.25″ drive appears as drive C. The CMOS settings need to be changed to 3 drives for it to work.

The expansion unit also had a printer card to accommodate a centronics style printer. The printer port on the computer is serial and maybe specifically set up for the data general printer. Both the serial ports on the computer are incompatible with IBM ports.

I added a spare CGA card and connected a CGA monitor. With the computer settings set to MONO the external CGA monitor becomes the default screen. The mode can be set to BW40, BW80, CO40, and CO80. If the mode is set to MONO the LCD is reactivated. Without the expansion unit connected, all of these modes work with the LCD. The external monitor makes life much easier.

I thought that an XTIDE card might work with the One. I just took one from an XT and plugged it into the expansion unit. DOS 5.0 booted, but there were some issues during the autoexec. That was enough to show the potential, though.

The system will also boot from the 5.25″ drive in the expansion unit. It will not boot from the rear floppy disk drive, which unfortunately doesn’t seem capable of formatting, although i have been able to write with it. Perhaps a gotek candidate.

I have been able to boot later generic versions of MS-DOS but they may have incompatibilities, eg the real time clock does not work.

I added an XTIDE card and programmed it with the large XT BIOS. The behaviour was a little unexpected, probably because the floppy disk implementation is not 100% compatible with an IBM PC. The Universal BIOS has trouble associating the drive with drive letters often confusing the flash disk with the third floppy. Selecting floppy drives by letter at startup also resulted in boot failures.

The XTIDE Universal BIOS does seem to be a little befuddled by the machine. Selecting the boot drive by typing a letter sometimes worked, but at other times produced baffling results. Curiously, invoking the menu and then using the arrow keys to select the boot drive from that menu worked fine. Perhaps the relevant data is reread at that point; only a universal BIOS expert would know.

Also, fortunately, the Universal BIOS will allow the system to boot from any of the floppy drives – as long as it is selected from the Universal BIOS menu.

MS-DOS 3.2 is limited to 32MB partitions, which is a little tight. This is probably not a major issue for this machine which is likely to have only occasional use. I could not get the card to boot, but it worked fine otherwise.

I set up a second CF card with DOS 5.0. I was able to make this one bootable and i could set up a full 512kB partition. There is no specific version of MS-DOS 5.0 for the One, so there are a few places where IBM incompatibility rears its head. Firstly the battery backed real time clock does not work, and secondly MS-DOS 5 seems to politely ignore the incompatible serial ports.

With XTIDE and Universal BIOS there are a variety of oucomes depending on the operating system and the boot drive:

OS	Boot Drive	Notes
MS-DOS 2.1	A 3.5″ Front Internal	Boots. Can access floppy drives A(front), B(rear), C(5.25″). Appears to not have hard disk support. Was unsuccessful formatting C.
MS-DOS 2.1	B 3.5″ Rear Internal	Boots. Can access floppy drives A(rear), B(front), C(5.25″). Appears to not have hard disk support. Was unsuccessful formatting C.
MS-DOS 2.1	C 5.25″ External	Not attempted.
MS-DOS 2.1	CF Card	Appears to not have hard disk support.
MS-DOS 3.2	A 3.5″ Front Internal	Boots. Can access CF card with 32MB disk as D. Can access floppy drives A(front), B(rear), C(5.25″). Can write to rear drive but not format. Can format 5.25″ drive and write.
MS-DOS 3.2	B 3.5″ Rear Internal	Boots. Can access CF card with 32MB disk as D. Can access floppy drives A(rear), B(front), C(5.25″). Can write to rear drive but not format. Can format 5.25″ drive and write.
MS-DOS 3.2	C 5.25″ External	Boots. Can access CF card with 32MB disk as C. Can access floppy drives A (5.25″), B(front), D(rear). Can write to rear drive but not format. Can format 5.25″ drive and write.
MS-DOS 3.2	CF Card	Does not boot. Have to boot from floppy. Then card can be accessed. See above.
MS-DOS 5	A 3.5″ Front Internal	Boots. Can access CF card with 512MB disk as C. Can access floppy drives A(front), B(rear), D(5.25″). Can write to rear drive but not format. Can format 5.25″ drive and write.
MS-DOS 5	B 3.5″ Rear Internal	Boots. Can access CF card with 512MB disk as C. Can access floppy drives A(rear), B(front), D(5.25″). Can format 5.25″ drive and write.
MS-DOS 5	C 5.25″ External	Boots. Can access CF card with 512MB disk as C. Can access floppy drives A(5.25″), B(rear), C(front). Can format 5.25″ drive and write.
MS-DOS 5	CF Card	Boots. Can access CF card with 32MB disk as C. Can access floppy drives A(front), B(rear), D(5.25″). Can format 5.25″ drive and write.

The rear drive seems to have a strange fault that allows writes but prevents format. May just be in the detail of the format program. The drive system is not 100% IBM compatible.

When formatting DOS 5 seems to treat all drives as 360kB by default. It may be possible to use format options to override but i found it very reluctant. Use driver.sys in config.sys to create new drives E and F that are 720k. Required on any DOS 5 boot disk.I thought that an XTIDE card might work with the One. I just took one from an XT and plugged it into the expansion unit. DOS 5.0 booted, but there were some issues during the autoexec. That was enough to show the potential, though.

I have been able to boot later generic versions of MS-DOS but they may have incompatibilities, eg the real time clock does not work.

All up, it’s a pretty complex picture!

I thught there may be a performance hit from using the expansion unit so i ran the performance test that is in checkit. The video speed is a little faster on the internal screen. Of course this may be due to the graphics implementation.

DG One XTIDE

Posted on January 26, 2026February 1, 2026 by Graham

I added an XTIDE card and programmed it with the large XT BIOS. The behaviour was a little unexpected, probably because the floppy disk implementation is not 100% compatible with an IBM PC. The Universal BIOS has trouble associating the drives with drive letters often confusing the flash disk with the third floppy. Selecting floppy drives by letter at startup also resulted in boot failures.

Curiously, invoking the menu and then using the arrow keys to select the boot drive from that menu worked fine. Perhaps the relevant data is reread at that point; only a XTIDE Universal BIOS expert would know.

But, fortunately, the Universal BIOS will allow the system to boot from any of the floppy drives – as long as it is selected from the Universal BIOS menu.

With XTIDE and Universal BIOS there are a variety of outcomes depending on the operating system and the boot drive:

OS	Boot Drive	Notes
MS-DOS 2.1	A 3.5″ Front Internal	Boots. Can access floppy drives A(front), B(rear), C(5.25″). Appears to not have hard disk support. Was unsuccessful formatting C.
MS-DOS 2.1	B 3.5″ Rear Internal	Boots. Can access floppy drives A(rear), B(front), C(5.25″). Appears to not have hard disk support. Was unsuccessful formatting C.
MS-DOS 2.1	C 5.25″ External	Not attempted.
MS-DOS 2.1	CF Card	Appears to not have hard disk support.
MS-DOS 3.2	A 3.5″ Front Internal	Boots. Can access CF card with 32MB disk as D. Can access floppy drives A(front), B(rear), C(5.25″). Can write to rear drive but not format. Can format 5.25″ drive and write.
MS-DOS 3.2	B 3.5″ Rear Internal	Boots. Can access CF card with 32MB disk as D. Can access floppy drives A(rear), B(front), C(5.25″). Can write to rear drive but not format. Can format 5.25″ drive and write.
MS-DOS 3.2	C 5.25″ External	Boots. Can access CF card with 32MB disk as C. Can access floppy drives A (5.25″), B(front), D(rear). Can write to rear drive but not format. Can format 5.25″ drive and write.
MS-DOS 3.2	CF Card	Does not boot. Have to boot from floppy. Then card can be accessed. See above.
MS-DOS 5	A 3.5″ Front Internal	Boots. Can access CF card with 512MB disk as C. Can access floppy drives A(front), B(rear), D(5.25″). Can write to rear drive but not format. Can format 5.25″ drive and write.
MS-DOS 5	B 3.5″ Rear Internal	Boots. Can access CF card with 512MB disk as C. Can access floppy drives A(rear), B(front), D(5.25″). Can format 5.25″ drive and write.
MS-DOS 5	C 5.25″ External	Boots. Can access CF card with 512MB disk as C. Can access floppy drives A(5.25″), B(rear), C(front). Can format 5.25″ drive and write.
MS-DOS 5	CF Card	Boots. Can access CF card with 32MB disk as C. Can access floppy drives A(front), B(rear), D(5.25″). Can format 5.25″ drive and write.

The rear drive seems to have a strange fault that allows writes but prevents format. May just be in the detail of the format program. The drive system is not 100% IBM compatible.

All up, it’s a pretty complex picture!

My XTIDE card does not have a rear facing slot to allow the CF cards to be easily changed. Often, i have to make do with what we can economically get in Australia. XTIDE does support two cards though, and there is plenty of space in the hard drive bay to house them. MS-DOS 3.2 does not see the 32MB drive, but DOS 5 sees both.

With a large hard disk, the first directory listing can take a long time. This is particularly noticeable on my PCs that have 2GB partitions. This effect seems accentuated on this machine and is very noticeable with the 512MB partition. I suspect that the bandwidth using the expansion unit is much lower than with the built-in expansion bus of the IBM PC and similar machines. Nevertheless, it is quite useable.

DG One Multifunction Card

Posted on January 26, 2026January 26, 2026 by Graham

The Expansion unit only has 6 slots and one of those is occupied by the connection to the One. One is required for the Floppy Disk Drive controller and another was occupied by the Hard Disk Controller, but that has been swapped for an XTIDE. Another was occupied by a printer card. Then i added a CGA card. One slot remained.

I really wanted to add a game port and a couple of IBM compatible serial ports (ideally one for a mouse and one for Kermit serial communication); the native com ports are not compatible. The easiest way to do this is to replace the original printer card with a multifunction card and an additional I/O panel. It may be possible to use the multifunction card’s floppy disk controller in place of the original, but i have disabled it for now.

I have used a CA9342 multifunction card. This card is 16 bit, but i expect that the 16 bit operation is limited to IDE, which i won’t be using. I disabled IDE and FDC. Obviously it is from a later era, but so is the XTIDE card. It could be replaced with an older card – one that could provide another 128kB of RAM would be interesting.

The Serial Ports were set to COM3 and COM4. This will provide two PC compatible com ports. The printer is set to LPT1 and the game port is also enabled. The second serial port and the game port connectors are mounted on a second I/O panel.

Parallel port enabled	JP2	pins 1 & 2 closed
Parallel port disabled	JP2	pins 2 & 3 closed
Serial port 1 address 3F8 – 3FFh select	JP3	pins 1 & 2 closed
Serial port 1 address 3E8 – 3EFh select	JP3	pins 2 & 3 closed
Floppy drive interface enabled	JP4	pins 1 & 2 closed
Floppy drive interface disabled	JP4	pins 2 & 3 closed
Serial port 2 enabled	JP5	pins 1 & 2 closed
Serial port 2 disabled	JP5	pins 2 & 3 closed
Parallel port address 378 – 37Fh select	JP6	pins 1 & 2 closed
Parallel port address 278 – 27Fh select	JP6	pins 2 & 3 closed
Serial port 2 address 2F8 – 2FFh select	JP7	pins 1 & 2 closed
Serial port 2 address 2E8 – 2EFh select	JP7	pins 2 & 3 closed
Game port enabled	JP8	pins 1 & 2 closed
Game port disabled	JP8	pins 2 & 3 closed
Serial port 1 enabled	JP9	pins 1 & 2 closed
Serial port 1 disabled	JP9	pins 2 & 3 closed
IDE interface enabled	JP10	pins 1 & 2 closed
IDE interface disabled	JP10	pins 2 & 3 closed
Serial port 1 interrupt is IRQ3	JP11	pins 2 & 3 closed
Serial port 2 interrupt is IRQ3	JP11	pins 1 & 2 closed
Serial port 2 interrupt is IRQ4	JP12	pins 1 & 2 closed
Serial port 1 interrupt is IRQ4	JP12	pins 2 & 3 closed
Serial port 1 interrupt is IRQ5	JP13	pins 2 & 3 closed
Serial port 2 interrupt is IRQ5	JP13	pins 1 & 2 closed
Serial port 1 interrupt is IRQ2	JP14	pins 2 & 3 closed
Serial port 2 interrupt is IRQ2	JP14	pins 1 & 2 closed
Parallel port interrupt is IRQ7	JP15	pins 1 & 2 closed
Parallel port interrupt is IRQ5	JP15	pins 2 & 3 closed

I ran checkit to check the configuration.

MS-DOS 5 does support COM3 and COM4 but can’t see the native One ports, so it labels COM3 and COM4 as COM1 and COM2, respectively. Checkit calls them by names based on their addresses. COM4 (that’s what you type into Kermit) works under MS-DOS 5 but COM3 does not. It only transmits.

MS-DOS 3.2 does not support COM3 and COM4 but Kermit still allows them to be selected, albeit with assumptions about addresses. I found the COM3 worked fine, but curiously COM4 would only transmit.

Once again the IBM incompatibility makes everthing flaky. Checkit reports a missing interrupt. It is what it is.

The joystick shows up and tests fine in Checkit. It does not always work in practice. It works great, for example, with Cosmic which is a space invaders style game.

DG One Software

Posted on January 24, 2026February 1, 2026 by Graham

The software situation is quite amazing – not so much for the quantity of it, but for the associated manuals which are substantial.

All the original disks have been imaged. The Flight Simulator II disk is copy protected so an IMD/IMG is not good enough; an SCP is required. The Overhead Express disk that i grabbed from the web needs to be written from the IMD; it is not enough to just grab the files.

Package	Disks	Manual	Notes
MS-DOS 2.1 OEM	2 original disks	2 manuals 1 key overlay	Tested and works.
Diagnostics	1 original disk		Tested an works. Has a hard disk formatter.
MS-DOS 3.2 OEM	Disk images available on internet	3 manuals	Tested and works.
GW-Basic OEM	On OS Disk	1 manual
Micropro Wordstar 3.3 OEM	3 original disks	6 manuals, 2 reference cards	Tested and works but limited to mono display. A generic copy of wordstar works with CGA as well.
Sorcim/IUS Supercalc 3	1 original disk	1 manual, 3 reference cards	Tested and works.
Sorcim/IUS Easywriter II	1 original disk	1 manual	Tested and works.
Ashton-Tate Framework 1.1 OEM	5 original disks	2 manuals, 1 key overlay
Micropro Infostar+	Only a Sanyo MBC 550 OEM version downloaded	4 manuals 2 reference cards
BPS Overhead Express	Data General Version downloaded	1 manual, 1 reference card	Tested and works. The floppy disk must be in drive A even when running from hard disk.
subLogic Flight Simulator II OEM	1 Original disk	manual, maps, reference card	Tested and works. Run from a floppy written from SCP.
SSI WordPerfect OEM	Only a generic version 3 download.	1 manual	Tested and works.
Digital Research CP/M OEM		1 manual

A full list of software is here, but it is not easy to tell if all of these are OEM versions and to what degree they may have been modified to work with the One:

dg-one-softwareprograms Download

The DG OEM version of wordstar always changes to the MONO screen mode when it executes which means it can’t be used on the external CGA screen. The non-OEM version works in either mode.