Date   : Wed, 08 Nov 2006 05:26:21 -0600
From   : julesrichardsonuk@... (Jules Richardson)
Subject: DFS on 3.5inch - Is this supposed to work?

Jason Watton wrote:
> For this very reason, Jonathan, you must *not* state:
> 
>> Another matter to know is that very few PC disk controllers can
>> actually do single density encoding. The vast majority only
>> understand MFM and many PCs have crippled BIOSes that only allows
>> reading and writing of 512-byte sectors.
> 
> as *fact*:
> 
> (a) The first statement (IMHO) is *false*, although 'very few' is vague.
> (b) The second statement (IMHO) is *false*, although 'many' is vague.
> 
> *Please*, I'm begging you, don't perpetuate this myth. You are putting 
> people off trying because of the force of your conviction.

OK, so my perspective:

I do a fair bit of data recovery work from old FM-only systems. I talk to 
quite a few people who do a *lot* of data recovery work from old FM-only 
systems as data recovery is their primary source of income.

Most PCs *will not* work properly with FM disk encoding. For a machine built 
around 2000, there's a reasonable chance of finding a motherboard with 
built-in floppy controller that'll read FM data, but won't write it reliably. 
Older motherboards tend to have built in controllers which won't read or write 
FM reliably at all, and almost all expansion card floppy controllers (as found 
in even older machines) won't read or write FM either. After all, it wasn't 
part of the original PC spec, so nobody ever had a reason to include it.

With much newer systems the picture's apparently a little better, which is 
pretty amazing - maybe because there's far less variety in motherboard 
chipsets than there used to be, and the few survivors happened to be the 
better manufacturers. Who knows. Of course then you soon start getting into 
the territory of systems which don't even *have* the ability to use a floppy 
drive...

So, across the whole spectrum of PCs, according to the experience of myself 
(and others even better qualified than me to say) most *will not* happily read 
and write FM data. For newer boards the situation appears to be better - but I 
for one can't justify spending money on random motherboards to see which work, 
and ability (or otherwise) to handle 25 year old disk technology isn't 
normally one of the things mentioned in the downloadable manual :-)

Regarding FM ability but BIOS/controller which only handles 512 byte sectors - 
that's a new one on me, to be honest. I've not yet found a system that'll 
handle FM but refuses to do non-512 byte sectors, but it's certainly possible 
that they exist (there are certainly a lot of broken controllers out there 
which won't handle more than one drive, despite the PC always being able to 
support two - so it's entirely possible that they're crippled in other new 
ways as well). My first test is always whether it'll write FM reliably, and if 
it doesn't it goes in the bin :-)

cheers

Jules