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. GerritReceived on 2019-01-04 12:00:03
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