On 1/4/19 11:57 AM, André Fachat wrote: > > > 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. I know... You could have done the same with MFM, but no one did for some reason. And it was hailed as a great development when they came with different speed zones on IDE drives. Called 'Zone Bit Recording' back then. My reaction back then was 'had this on floppies years ago... what else is new?'. GerritReceived on 2019-01-04 13:00:47
Archive generated by hypermail 2.2.0.