MFM/RLL data recovery

[Randy McLaughlin]

From: "Jules Richardson" <julesrichardsonuk at yahoo.co.uk>
Sent: Monday, April 04, 2005 7:23 PM
> On Mon, 2005-04-04 at 19:00 -0500, Randy McLaughlin wrote:
>> From: "Vintage Computer Festival" <vcf at siconic.com>
>> Sent: Monday, April 04, 2005 6:14 PM
>> > On Mon, 4 Apr 2005, Randy McLaughlin wrote:
>> >
>> >> If you are trying to recover files you are probably wasting your time,
>> >> the
>> >> XT controllers used unique formatting and you will never read the data
>> >> off
>> >> of the drives without using controllers indentical with ones used
>> >> originally.  It is not good enough to use the same brand or even 
>> >> chipset.
>> >
>> > This doesn't make much sense.  Can you please explain further?
>> >
>>
>> With Vintage as a domain name you should be familiar with the fact that
>> standards develop slowly.
>>
>> Hard drive interfaces for the PC "standardized" with the AT, before that
>> people did what ever they wanted.  Sometimes one controller would read a
>> disk from a different type of controller but it was just luck.
>
> I was confused by the statement too. Are you saying that the same
> *model* of controller won't necessarily work (due to different
> tolerances in components say) - or just that different controllers that
> happen to use a few common chips won't work?
>
> The former would be a little alarming - the latter makes much more sense
> and would seem like a given. (Maybe that's where Sellam was getting
> confused?)
>
>
> cheers
>
> Jules

The incompatibilities are not a tolerance problem, when the same chipset is 
used the BIOS can be different and not be compatible.  But I've always found 
that the same model controllers were interchangeable with no problems.

A few times I've seen different PC controllers from the same manufacturer 
(i.e. WD or whatever) work from one model to another but not be able to boot 
without a low-level formatting (booting from a floppy allows access).

Other times no compatibility at all and must be low-level formatted to do 
anything.

As was pointed out if you know the drives were formatted on a 8 bit 
controller just set the BIOS to no hard drive and don't even try the 16 bit 
controllers, they would just be a waste of time.  Your best bet would be to 
try different 8 bit cards and boot to a floppy then do a "dir c:", repeat 
until you've tried all cards.


Randy
www.s100-manuals.com