Re: Did Commodore cheat with the quad density floppies?

Am 3. Januar 2019 20:01:30 schrieb "Mike Stein" <mhs.stein@gmail.com>:

> I wonder if part of the answer to Andre's original question may be the fact 
> that Bits per inch is not necessarily the same as Flux transitions per 
> inch/mm...

Absolutely. 300 Oersted media had 5900 flux transitions per inch, which 
gives 2900 bpi using FM due to the many clock bits needed, or 5900 bpi 
using MFM. QD was the same media, only was defined for 96/100 tpi instead 
of 48 tpi.

Commodore GCR 170k used 250kHz write frequency,  thus the same 5900 flux 
transitions per inch, i.e. 4us bit cells.
Commodore GCR 500k used 375kHz writes, which increases ftpi by 50% and 
reduced bit cell size by 33%. Which seems to be out of spec with all Media 
specifications I found.

André

André