A quick note for those who use the HDD controller on a MFM or RLL drive to do a low level format. Depending on the size, it can take a REALLY long time. I had to do it quite a bit in the 80's and some drives like say 40MB could take a good 36+ hours. Worked like a charm, but is a very slow method. The very rare ADRT required any RLL drive hooked up to it be low level formatted but was very quick at the job. I remember doing several 30-80 MB drives in less than a couple hours each. Well worth it if you can find one, but don't use an MFM drive with it. It will work, but the life of the drive will drop like mad. I found that out the hard way.
On a side note, you can still use that debug command with one other little option (I'm not going to say what it is), to start a low level format on a modern IDE drive and make it so the drive cant be read under any normal recovery. To fix it so it will read again, one has to pull the platters out and use a special machine used in crashed HDD recovery labs while known what the problem is to correct it. I actually had a job back in the 90's where I had to do this to many drives to prevent data from ever being read form them. In essence it destroys the drive unless you are willing to spend $5,000.00+ to fix it and even know what the problem is as well as the solution. It was the perfect way to leave a drive functioning but show it had a "mysterious" crash. I was not at all pleased with that job to say the least.
