What is mfm drive

The MFM drive was designed to use only 17 sectors per track and forcing it to use 26 or more could permanently damage it. You may get 30MB out of a 20MB drive, but it won't last too long.

What seems to happen to most is that the format routines work fine, they load the data and everything seems ok, but after a few days or weeks all of a sudden they can't access their drive or they experience data corruption problems. Basically any good drive 'bible' or 'encyclopaedia' will list the various drive models and their encoding techniques.

These same books will also usually list the encoding technique employed by the various disk controllers. Just look up your drive model types and be sure the encoding technique is the same for both disk and drive.

Any local service organization should be able to help too. Regards, Mike Thomas. So far so good. But your source is wrong. What these things do is "encode" information into electrical pulses. When reading, the processing is reversed. Floppy drives still do. MFM was relatively simple to implement, and quite robust.

RLL Run Length Limited encoding used the same electrical interface and cables but a different data format much as Morse Code and Baudot code are different. RLL did, however, require a very accurate drive mechanism. Early attempts to increase speed and storage capacity by adding an after-market RLL controller to an MFM drive system often resulted in poor reliability.

So it was more or less a hybrid between stepper and rotary voice coil actuator. It had an optical encoder disc. KryoFlux for HDDs would be pretty cool. I remember having to recover the data fr an accountant way back in the day.

The spindle motor had died so with some creativity I drilled and tapped the center shaft the attached a high speed drill with a speed controller. Once that was done copied all the data off on to another drive and had one really happy client that learnt it was a good idea make backups. He wrapped a string around the motor shaft and gave it a pull at power up, just like starting an old outboard motor!

Drives were expensive enough that he did this for a year or so! Yeah, I remember about or so getting a 20 MB drive free at a flea market. The case had been pried open. To start the drive spinning, I had to insert my index finger and manually spin the exposed top platter.

Copied almost all the files off it. Close to one I had to do. I would switch on the power, reach under the drive and manually spin up the drive. Then I would copy off as many files as I could until the disk decided to hang up again.

Then I would repeat the process, and eventually got all their files off. My first hard disc was bought not working. Western Digital. It had a faulty chip that was WD specific. A quick search in the phone book, found their phone number in Scotland and rang them up. The guy I spoke to stuck two of the chips in an envelope and posted them to me gratis, changed the chip and it worked wonderfully, I still have the second one somewhere.

Fluke might still do that: A high precision resistor opened in mine way out of warranty. They mailed a new one. I guess it depends on who you talk to and their mood.

Before the WWW. Western Digital had the best tech support. They had a dialup BBS with files to download. If you needed documents you looked them up on the BBS then made note of their numbers.