Re: MFM drive gone nuts

----- Original Message ----- 
From: "smf" <smf@null.net>
To: <cbm-hackers@musoftware.de>
Sent: Wednesday, July 23, 2014 12:25 AM
Subject: Re: MFM drive gone nuts


> >Not quite; we're talking about the same computers, interface and file
> >systems.
>
> The MFM controller card has a CPU and it's own proprietary software,
> making it just as important as your motherboard and filesystem.
> How the MFM controller works isn't part of the ISA or ST506 standard, the
> same as the format and the filesystem of a floppy disk isn't part of
> shuggart.
--
Yes, but my point was that, unlike expecting a PC to be able to read an
Amiga or PET disk, I think one could reasonably expect a given model of PC
to be able to read a hard disk from another equivalent model PC using the
same ST-506 interface, drive specs, OS version etc. with nothing more than 
perhaps a simple BIOS configuration change, but you'd have to be pretty 
lucky...

There were certainly also numerous different floppy controllers, but the
diskettes were nevertheless interchangeable.

Similarly, many controllers were also restricted in the makes/models of
drive they could support, so if your drive failed or you wanted to upgrade
you'd quite possibly have to replace the controller as well.

> The only way to fix the problem would have been to force all MFM
> controller cards to work the same way.

They wouldn't have to *work* the same way, but a common 'standard' low level
format would have been nice, and that's one of the issues that IDE
effectively resolved by making the low level format and geometry irrelevant
and presenting a more or less standard logical and physical interface to the
bus.

>>That was probably the best thing about IDE; it combined the controller and
>>drive in one package with a common logical interface;
>
> You still have the same problem if the controller card on the IDE drive
> dies. It's worse as there is no guarantee the interface is the same and
> the controller firmware is on the drive. Unless the firmware on the drive
> is compatible with the controller you have fitted then you won't get
> anything working unless you have access to the tools used to load the
> firmware in the factory (which is generally unlikely).

We're picking nits here; since the controller and drive electronics are the
same board in an IDE drive, if  the 'controller' part of the pcb fails then
the drive is a brick, and the only way to get at the data is to repair or
replace the board, exactly the same as if the board on an ST-506 drive
fails.

The frustrating issue with the ST-506 drive is that the drive can be 100%
functional but you may not be able to find a system that can read its
low-level format, or at least it can be a real PITA.

Compared to the chaos of hard disks in early PCs, the 'twisted' cable is a
total non-issue...

m


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