Am 4. Januar 2019 11:48:45 schrieb Gerrit Heitsch <gerrit@laosinh.s.bawue.de>: > On 1/4/19 10:41 AM, André Fachat wrote: >> >> >> Am 4. Januar 2019 10:26:14 schrieb André Fachat <afachat@gmx.de>: >> >>> >>> >>> 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. >> >> And, BTW, MFM ist actually more efficient than Commodore GCR. >> >> MFM uses 16 cells at 500kHz, i.e. 16 x 2us = 32us per byte. >> Commodore GCR uses 10 cells at 250kHz, i.e. 10 x 4us = 40us. > > But the final drive implementation still resulted in Commodore drives > with their custom logic fitting more data onto the same media than > compared to MFM drives using a standard controller. That was mostly due to different speed zones so Commodore could store more data on outer tracks. André >Received on 2019-01-04 12:01:37
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