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. FrankReceived on 2019-01-02 17:00:52
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