MFM/RLL data recovery

[Randy McLaughlin]

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?
>
> -- 
>
> Sellam Ismail                                        Vintage Computer 
> Festival
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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.

Most hard disk controllers formatted to 17 sectors of 512 bytes per track 
but that doesn't say much about how it is formatted at the hardware level 
(bit for bit).  Another point is that before the AT the drive geometry was 
normally kept on the drive and different controllers stored the information 
differently.

With the PC many people hooked up drives before the XT came out but once IBM 
came out with the AT they had chosen a "standard" hard drive controller 
everyone worked to emulate until RLL controllers came out.  Even controllers 
like the Everex controllers that did track buffering to allow 1:1 interleave 
were still "compatible" with the AT formatting.

If you have an MFM drive used on an AT or better you have a good chance of 
reading it on any AT or better system with most any controller.

RLL or 8 bit based systems have no such "standard".


Randy
www.s100-manuals.com