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MFM Controllers and Data Recovery

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First post, by Droidekafan

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Hi all, looking for some advice on MFM hard disks and controller compatibility.

So I do some work in data recovery and we occasionally still get MFM hard disks in which we don't have the hardware to recover at the moment. I have my personal vintage machines lying around and out of curiosity I want to attempt to recover some of these disks.

However as you all likely know, controller compatibility can be an issue with MFM/RLL drives. I don't have much experience in this area so I wanted to know if anyone has ideas as to what controller would be the best option for the widest compatibility and ability to recover the most types of drives? I was planning on using spinrite and sending data over laplink to a more modern PC if I can get the drive working on a compatible controller.

I only have 1 MFM drive controller in my collection at the moment, in my PC AT 5170 with a functioning MFM drive. However I'm not sure how compatible the stock IBM storage controller would be especially with newer/larger drives.

There's also the MFM hard disk emulator; https://decromancer.ca/mfm-emulator/
Anyone have experience with one of these?

Thanks all

Reply 1 of 4, by maxtherabbit

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For professional data recovery you're better off using the gesswein emulator to image the disk instead of connecting the drive to a real vintage controller. The emulator can image MFM encoded drives from any controller type. The only issue would be if the drive was RLL, which I believe it doesn't support.

Reply 2 of 4, by Droidekafan

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maxtherabbit wrote on 2025-04-22, 13:02:

For professional data recovery you're better off using the gesswein emulator to image the disk instead of connecting the drive to a real vintage controller. The emulator can image MFM encoded drives from any controller type. The only issue would be if the drive was RLL, which I believe it doesn't support.

That was my thought too, any experience with them especially regarding compatibility? Also I don't believe these are compatible with RLL drives, is there any option on that front?

Cheers

Reply 3 of 4, by digger

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I can wholeheartedly recommend this video by Adrian Black (of the YouTube channel "Adrian's Digital Basement") about this topic.

He shows how such a device can be used both to back up data from a physical MFM drive, as well as emulate an MFM drive in a host computer.

The MFM Hard Disk Reader/Emulator that he uses in the video is a different one than the one you linked to. You can find more info about that device here: https://www.pdp8online.com/mfm/

Not sure how the two different hardware emulation solutions compare.

Reply 4 of 4, by Dan Solo

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Yeah, MFM/RLL compatibility is always tricky, especially if you’re trying to use stock IBM controllers. The Gesswein emulator does a solid job for imaging, but you’re right that it won’t handle RLL.

If you’re just experimenting it’s fun to mess with old controllers and emulators, but if you’ve got disks that really matter, you might want to look into a pro recovery service. Companies like SalvageData salvagedata.com still take in MFM drives, and they’ve got the hardware setups to bypass a lot of those controller issues entirely. Could save you a lot of headache if the data’s important and you don’t want to risk degrading the platters further.

For tinkering though, the decromancer emulator is probably the cheapest way to dip your toes in.

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