> On 17 Apr 2026, at 08:07, Francesco Messineo <francesco.messineo_at_gmail.com> wrote: > >>> Minor inaccuracy inherited from the previous video is the visualisation of the tracks on disk layout. 1541 is an 80 track drive but with the head it is equipped with and double-stepping it is made to be effectively 40 track drive, not 35 track one. CBM DOS simply does not use the innermost five tracks, presumably as a reliability safety margin. This means the visualisation, which shows the tracks spread evenly across the surface with no unused portion is not really correct. > > all correct, however I presume the use of only 35 tacks was chosen to > remain compatible with the 4040 formatted disks. The SA-390 > (effectively a SA-400 without controller) used on the 2040/3040/4040 > could only use 35 tacks. That would depend on whether the compatibility was meant to be both ways. There should be no problem reading 35 tracks formatted disks if 40 tracks were used in 1541. It's all soft numbering there. > I *think* the 1541 firmware could have been tweaked to use either 35 > or 40 tacks and in facts the old Speeddos plus mod allowed us to > format up to 40 tracks. Yes, that's purely software limitation. DolphinDos formats 40 tracks at will (provided the medium is a quality one) and gives 749 BLOCKS FREE instead of 664 we all know and remember. > However even back in the '80s I recall the > upper additional tracks weren't super reliable (maybe some gaps would > need better tuning when going over track 35?). That's precisely my point. At slower linear speed on the upper (inner) most tracks, the reliability could suffer, but since I used to avoid crappy media, which used to leave dirt on the head etc. I hardly encountered any. > 1541 firmware uses "half track" steps to try reading sectors in > presence of read errors. True. And it makes sense, doesn't it? -- SD!Received on 2026-04-22 14:00:02
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