Also, the GCR format is much more reliable than the MFM format. With a small number of consecutive zeros, the error rate is less. On Wed, 2 Jan 2019, Francesco Messineo wrote: > On Wed, Jan 2, 2019 at 3:40 PM André Fachat <afachat@gmx.de> wrote: >> >> Hi there, >> >> I was looking at floppy disk recording schemes and I am wondering if the >> 8050/8250/1001 floppy disk format with over 500kB per side was actually out >> of spec of even the Quad Density disks? >> >> The recording frequency was increased from 250kHz to 375kHz (× 1.5, for the >> innermost i.e. most critical track/speed zone). That resulted in a much >> increased number of bits per inch. See here: >> https://extrapages.de/archives/20190102-Floppy-notes.html >> >> What do you think? >> > > I'm sure you know it, but the best reference I've found on the net > about floppy disk drives is here: > > http://www.retrotechnology.com/herbs_stuff/drive.html > > First of all, 100 tpi drives have an offset recording window with > respect to 48 tpi drives. Track 0 is a bit closer to the outer edge of > the media with respect to the 48 tpi track 0 (or track 1 as CBM > counted them), but that doesn't really change much. The BPI rating of > the media isn't an absolute value imho (3000 for FM at 125Kbps and > 6000 for MFM at 250kbps are just what is achievable with these > modulations). I think the CBM designers just tried to pack as many > sectors as it was reliable. Original 2040 format on 48 tpi drive had > one sector more on one zone than the vastly more common 4040/1541 > format and I think they just decreased the later format by one sector > because it was a bit too unreliable. Same thing must have happened on > the 100 tpi drives, they tried to pack as much as was possible with > 300 oersted media. > Frank > > > wlevak@sdf.lonestar.org SDF Public Access UNIX System - http://sdf.lonestar.orgReceived on 2019-01-03 02:00:03
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