MFM Hard Disk Reader/Emulator

This page has information on the MFM hard disk reader and emulator I have been working on. The unit is intended to read MFM hard drives for archiving and to emulate one or two MFM hard drives to replace failing MFM drives. The image read from a real hard drive can be used for the emulation.

In theory the unit can emulate any MFM hard drive. In practice there are enough variations in how controllers use the drives that software changes have been needed to make it work with some systems. You will need to use a command line to operate the unit for reading disks and to configure it for emulating disks.

It should be able to read and save the raw transition data from most any hard drive using the ST506/ST412 interface. People are still running across formats it can't decode to sector data. For formats that are minor variations adding support doesn't take too long. For some controllers which did their own undocumented thing it can be significant effort to figure out the format. Handling physical to logical translation that some smart controllers did or any file system interpretation is outside the scope of this project.

Writing to real disks is experimental supported.

Tested configurations MFM web page update history

Manuals: MFM reader usage informationMFM disk emulator usage informationextracted data file to emulator file converter,  and Experimental write usage information. You may wish to start with example usage

The board has capacitors to give enough time to cleanly shut down when the host computer is turned off. Instructions for that feature: Power monitor usage information

I disclaim any warranty of merchantability or fitness for a particular purpose. I have been providing support on a time available basis which sometimes means I can't look at your issue for a couple of weeks. I also may not be able to figure out/fix the problem. Some of the issues were only solvable because the person had a logic analyzer and schematics were available for the controller so we could understand what strange things it was doing.

If you're still interested below are the prices.

I have boards again.

If this doesn't look like what you want there is another unit available from someone else. I have not used this unit. It is somewhat different than mine so verify it does what you want. When I looked at the pages it looked like it couldn't read an existing drive and the controller in your computer needed to be on the supported list for it to work.

Email me at link at bottom of page if interested. If outside USA either send me information on shipping method you wish or your address so I can verify shipping cost.

For bare boards you will need to order the parts from your distributor of choice.

The assembled boards have all parts installed except U11 and associated parts. For this board where pin function changes based on mode the EEPROM doesn't seem useful. I have been mounting the capacitors on the bottom. You may request other. This page shows more on the mounting the capacitors.

Forum and issue tracker

Issue tracker is here.

Forum for discussing this project is here,

If you have a board

See this page if you are assembling a bare board
See this page for testing a board you built or using an assembled board
If you are assembling the first revision of the board shipped in 2014 look at the above first then see the original assembly page. I am no longer updating that page. The software from the current board works on the original board also.

See this page for some historical information on the revision B development

Non English Documentation

These are what users wrote up on their use, not direct translation of my pages.


The Assembled Board

Old pages describing start of project

Feel free to contact me, David Gesswein with any questions, comments on the web site, or if you have related equipment, documentation, software etc. you are willing to part with.  I am interested in anything PDP-8 related, computers, peripherals used with them, DEC or third party, or documentation. 

PDP-8 Home Page   PDP-8 Site Map   PDP-8 Site Search

Mirror site if this site is slow