Early 3.5" Floppy Drives - test-drb@ccmp.vtda.org

15 Dec 2005

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Subject: Re: Early 3.5" Floppy Drives
   From: "Chuck Guzis" <cclist at sydex.com>
   Date: Thu, 15 Dec 2005 17:43:09 -0800
     To: cctalk at classiccmp.org

On 12/16/2005 at 12:49 AM ard at p850ug1.demon.co.uk wrote:

   Any PC
controller that can do 720k 3.5" format can do 
 8" as it's the same data rate.  it's not what chips was  
I don;'t think you mean that!. The 720K 3.5" format is the same data rate 
as the 360K 5.25" format. You mean any controller that can do the 1.44M 
3.5" format (or for that matter the 1.2M 5.25" format), surely. Those are 
the same as the 8" data rate. 
Yeah, he did--sort of.  This assumes that the data separator can be
jiggered to deliver separated FM data at the same rate that it delivers
3.5" separated MFM data.   i.e., 8" FM has the same data rate as 720K 3.5"
MFM.

Although, I'm still puzzling over my databook's definition of pin 21, it
says "500 KHz for FM and 1 MHz for MFM" but makes no mention of write data
rate (i.e. mimifloppy vs. 8").   Could this be simply something left out? 
It's seriously incomplete.  What data book is it?

If anything it also forgets 250khz (older FM 5.25).

Look at the schematic from apnotes, the authors did make an effort to 
unhide information.  It's just a matter of following the logic. Having
more of the text would help but with slowpoke scanner 31 pages would 
take at least 4 hours.

Allison