FM is RLL, MFM is RLL, RLL is RLL! Fight me.

The EDS PC is a fascinating machine, but where we last left off, it didn’t have a functional hard drive. It has an ST-238R in it, which is an RLL drive with appropriate RLL controller card, but the drive did not seem all too happy last time we spun it up. In this episode, I want to try to rescue the data off the drive using David Gesswein’s amazing tool, but also, I want to learn a bit more about FM, MFM and RLL in general.

For more on the EDS PC:

For more about David Gesswein's excellent emulator, check here:

If you want to know more about the Centurion, the wiki is full of just about everything we know:

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Intro Music adapted from: Artist:
The Runaway Five Title:

Thanks for watching!

Chapters
0:00 How fast is too slow?
3:38 FM, MFM, RLL and the ever important… RLL?
10:48 Imaging an MFM drive (which is really RLL)
15:42 Imaging a not crap MFM drive (which is still actually RLL)
18:57 Imaging an RLL drive (which is… also RLL…)
23:00 Giving the RLL (not MFM) drive a shot
24:12 Giving the MFM (yes RLL) drive a shot
33:02 How fast is excellent?
36:24 Baby bunny!
37:15 Don’t anger the Youtube Gods…

[YT-branch]

Lol, I just knew AJ from Knight Rider Historians. I had no idea he was into vintage computing.

[stoojinator]

Funny how I haven't done a lowlevel format of an RLLor MFM drive since the late 80s, but I still remembere debug g=c800:5. Crazy what the brain stashes away.

I am loving your channel. It's got so much fantastic content. /spins propellar hat.

[ByteDelight]

This could easily have been an 80's video showing off the speed of the newly introduced harddrives! 😄
I love it! Nicely done David!

[doogie]

Back in the day our company took in many computers with RLL drive failures. Typically the data could be recovered using Norton Utilities. With such a reliability issue with RLL we would recover the data, install a MFM controller and restore the data to the ST-238R using MFM formatting. Given the cost of the drives at the time most customers were happy only loosing 10 megabytes of storage.

[steveb]

Whilst in FDISK you can check that the partition is also made active (usually option 5), then format c: /s /q (/q quick format if available)

[lucasgoldner]

Oh, the ironies of life, last night i had a sudden thought, what's the difference between MFM and RLL? I said to myself "welp tomorrow i'll look at it", and as magic, Usagi made made a video explaining it.😮

[televisionuser]

Maybe the first time I knew something you didn’t with the DOS stuff 😂

[johnrichardson]

I thought I was the last person alive that knew MFM and RLL

[Plarndude]

Hellorld! I’m fascinated and happy. 😊

[theantipope]

Wow, it has been 40+ years since I needed to care about this stuff. An RLL qualified drive like the ST238 (30MB, IIRC) *REQUIRES* an RLL capable disk controller! A normal MFM controller cannot read an RLL formatted hard disk.
If this is an ST238, it'll format to 20MB if you have a normal MFM disk controller, or 30MB if you have an RLL disk controller.
If you want the hard disk to be bootable, you need to use `format c: /s`
29:50 Okay, to make C; bootable, you need to switch to A:, then `sys c:`

[marksmith]

Use Macrium Reflect for full disk backups. Have even done ones with non DOS sectors which is very handy.

[Artimis.depressed]

30:57 by the way, running ‘format C: /s` has the same effect

[herauthon]

i know from ALTA .. that MFM disks can become RLL by the bios-formatter tool
the miniscribe 32Mb was actually a 20MB MFM - turned RLL (afaik)
- i might be wrang.. it is ALTA..

[scottpetersen]

Do the hard drive heads need to be parked on that drive? I forget when they were self parking?

[janklas]

No reason to fight. MFM and RLL are compatible in hardware. If you have a 20Mb Rll Disk, you can format it as a 30Mb RLL disk.

[CEverett]

"Format c: /s" to format with system

[williefleete]

Yea you need to bless the drive to make it bootable in DOS