On Fri, Jun 19, 2026 at 5:02 PM André Fachat <afachat_at_gmx.de> wrote: > > The original Shugart disk drives (SA390 for Apple II and Commodore as well, SA400 for PCs) could only use 35 tracks due to physical limitation. > Commodore probably wanted to keep compatibility with the older DOS. > > They could have gone beyond that with the QD drives (100tpi drives), but as I figured they were already above the floppy disk spec (see link posted earlier) they probably decided to not overdo it with the bit density. beyond as over track 77? Can the Micropolis 1015/1016-II do that? Or beyond as clock rate? I believe the 8x50 format is close enough to maximum transitions per inch of the old magnetic media. Standard FM/MFM controllers didn't even attempt to raise the clock rate on 96 tpi drives, they just formatted twice as many tracks of a 48 tpi drive. I believe this link contains very good information both about drives and magnetic media: https://www.retrotechnology.com/herbs_stuff/drive.html Commodore imho did an outstanding design for the era (considering the SA-390). Troubles started when the 1541 wasn't upgraded to use the fast serial port of the 6526 inside C64. But that's another story (and we got a whole lot of fast loaders in return). Frank IZ8DWFReceived on 2026-06-19 17:00:02
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