Hi,

I think XT-IDE BIOS supports at least 2 drives even on 286 era HW(It can support actually a lot more but I remember that AT class machines needed for the full number somewhere in the documentation), however the only 286 PC in my collection has a still working HDD in it(Going surprisingly strong despite its age, only a few bad sectors, unlike the monochrome monitor that it is attached to it which seems to have a mind of its own to decide whether to work or not 😁), so I had no reason to use such adapters in it.

However on the first picture I do notice a Battery Warning on the screen, a lot of batteries from this era has a tendency to leak, if it is one of such parts then I would consider replacing it before it leaks and damages the motherboard.

If you add an IDE card, it must be secondary, otherwise it will conflict with the MFM controller.

I don’t know what xtide might do with such a combo, but that is the starting point. It might even work.

After all, the first IDE drives pretended to be an MFM controller attached to the AT bus over a ribbon cable. The ide card just decodes the correct address and switched the bus through.

The MFM controller has an unpopulated connector for another mfm drive.

There *are* drive emulators for mfm controllers, they are just more niche and expensive, like this one:

https://www.drem.info/

As others point out, IDE adapters will need to be jumpered as secondary controllers to coexist with an MFM controller.

Depending on what your build intent is, straight up replacing the mfm storage might be the most appropriate and futureproof option.

On the flipside, the mfm drive emulator keeps the system more original.

There are options for every choice, but that choice is up to you.

wierd_w wrote on 2026-06-06, 14:32:

There *are* drive emulators for mfm controllers, they are just more niche and expensive, like this one

a new one is being cooked and progressing steadily https://github.com/MajenkoProjects/RTmFM should be super cheap since its based on $5 pico 1

Slightly different angle: the issue with MFM vs IDE is that both use system BIOS and so potentially conflict. SCSI on the other hand brings its own BIOS and so can co-exist with any MFM/RLL/ESDI/IDE config. It is also very forward-compatible, so you can take a larger newer drive and hook it up to a 16b ISA adapter (the ubiquitous Adaptec AHA1542 comes to mind). If you happen to have some of this stuff lying around it would be an easy option.

Wow, thank you very much for all the information! I'll start reviewing in depth, I see it's no trivial at all, with many options and pros/cons to consider.

Regarding possible disk size, I don't have it with me to check but probably the original 286 BIOS has the typical list of 50 C/H/S HDD configurations supported, topping on about 150MB. If not replacing/overriding the BIOS with another option I guess that's probably the limit, so if using something like a CF card, perhaps the most sane option is to use a 128MB model, or perhaps is possible to use a bigger one and just format it so the partition size remains under that limit?

I guess creating many partitions won't upper the limit, as it's a limitation on HDD size, not partition size, right?

I'm also thinking if the geometry the CF card shows the system (C/H/S) doesn't match exactly one of the options supported in the BIOS, perhaps it won't be detected at all?

Typically if you can match the heads and sectors, and pick the highest number of cylinders you can find in the table, drives will work but cut off at that capacity. It iis theoretically a thing that IDE drives cope with a translation themselves, where you just set the capacity to best match and it fudges the heads, sectors and cylinders to match. This gets the drive working in THAT machine, and allows one to partition and format it under that. But then when you move it to another machine you might get problems, unless you set the exact CHS that it was set up under.

XTIDE BIOS seems independent of physical interface, because you can put it on a network card hosted EEPROM, and have primary IDE on the motherboard or standard ISA I/O and have the secondary on a soundcard IDE or another I/O card set to IRQ 15.

However, I am not super familiar with how it sets itself up and whether it relies on autodetect which might be the sticking point with the MFM drive. Otherwise I would expect it to just work with a primary MFM and secondary IDE. Also there was a way to set up MFM drives which was a manual translation, double the heads, halve the cylinders etc, and it would work on THAT machine, so if another machine autodetected it, it might use native CHS when it wasn't formatted like that and have problems. Buuuut you usually only find weird stuff like that in machines that started life as floppy only or had HDD upgraded in MFM era.

So it's the usual, everything is perfectly standard and compatible unless it isn't.