Author: 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:

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.

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.

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.

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.

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 outcomes depending on the operating system and the boot drive:

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.

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.

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.

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.

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.

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:

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.

I have not found a CP/M-86 disk although i have seen it mentioned in forums. There is a CP/M programmers guide amongst the manuals that i have.

Some of the Data General communications mention a version of Unix but i have not found that either.

Most of the manuals do not seem to be online so i have some scanning to do!

Many generic IBM compatible apps work fine.