Post AWBxhfOfN9OPEZN2GW by mkgraham@mastodon.online
(DIR) More posts by mkgraham@mastodon.online
(DIR) Post #AWBwHKzUWFVmSjTblY by TechTangents@dialup.space
2023-05-30T20:24:42.832624Z
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I could use some input on this from anyone with more floppy drive experience, I was planning on making a video taking an in depth look at the issues with writing 360k disks in a 1.2M drive, the issue being the different in head widths being 40 and 80 track respectively.My theory for visualizing this was writing a 360k disk in a 40 track drive, but reading the flux using an 80 track drive to "oversample" "extra" track data to try to visualize the partial writes you get from the narrower 1.2M head on 40 track disks. When reading I thought the 80 track head would essentially read each track on a 360k disk twice, but instead it seems that the 80 track drives center the head on 40 track disks to the track because I get interleaved good and bad tracks when making the flux images in an 80 track drive. Almost like its reading a track and then the space between them.Does this sound right or familiar to anyone? I'd never tried this before and it didn't match what I expected. The images here are even from three different models of drives. (Teac FD-55GFR, Mitsubishi MF504A-375U, Mitsumi D509V3 respectively) and they all behave the same. Not being able to visualize the issue kinda puts a big hole in my plan for a video on this.
(DIR) Post #AWBxhfOfN9OPEZN2GW by mkgraham@mastodon.online
2023-05-30T20:33:39Z
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@TechTangents Hmm... I hadn't thought about it much before, but it makes sense to me that the 80 track drive would have every other track line up with the center of a 40 track. If you read one edge then the other instead you'd be more likely to get bad reads. I'm not sure how you'd get the visualization you want without intentionally misaligning your drive.
(DIR) Post #AWBxhgAWVDfpczlFrM by TechTangents@dialup.space
2023-05-30T20:40:38.193221Z
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@mkgraham It does make sense the drives would be made this way for sure. It does make it a little surprising there are write issues. Between that and the higher power head I would think it would probably mostly work out. Maybe the problem ends up being more noticeable with the writing/reading drives being slightly out of calibration.
(DIR) Post #AWByN6NPxzqgmdXoUC by mkgraham@mastodon.online
2023-05-30T20:44:56Z
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@TechTangents Could be. One specific thing I remember hearing is that you shouldn't write to a disk that was formatted on a 40-track drive using an 80-track drive because it might not be able to properly overwrite the existing flux, but it's one of those things I always took for granted and never tested out.
(DIR) Post #AWByN77VCeiD5Z6cJk by TechTangents@dialup.space
2023-05-30T20:48:08.485267Z
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it is true I've encountered issues stemming from it. That was the crux of why I wanted to make the video, it's not something that everyone has tried or fully understands. But it looks like it will be too difficult to visualize the issue so I'm probably going to skip it for now
(DIR) Post #AWC8iTT0JQz61EzGSW by vwestlife@mastodon.social
2023-05-30T22:04:51Z
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@TechTangents Anecdotally it seems that it's mostly the old full-height drives which have problems reading 360K disks that were written to using 1.2MB drives. Peter Norton blamed the problem on older 1.2MB drives not being aligned properly, and by 1989, floppy drive manufactuers claimed to have solved the compatibility problems between 1.2MB and 360K drives, possibly by beginning to use the narrower 80-track heads even on 40-track drives, although I don't know that for sure.
(DIR) Post #AWCCxIneeaht62yLSa by philpem@digipres.club
2023-05-30T23:08:19Z
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@TechTangents I've noticed the same; the authority would be the ECMA standards for 5.25in floppies. That'd probably be ECMA-70 and ECMA-78:https://www.ecma-international.org/publications-and-standards/standards/ecma-70/https://www.ecma-international.org/publications-and-standards/standards/ecma-78/Per page 22 of each, the tracks are spaced at (n/96)*25.4mm intervals (96tpi) for 80tk and (n/48)*25.4mm for 40tk. That's not counting the 8-track (96tpi) offset between each side.The track is ~half the width on 96tpi (0.155mm vs. 0.3mm nom). If I've got the maths right, tracks should be side by side.
(DIR) Post #AWCCxJTU94ARBmXkf2 by philpem@digipres.club
2023-05-30T23:09:51Z
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@TechTangents Winding all that maths up - I can't explain why you get a good read followed by a bad read, but I have had discs which had two good reads. My guess is it's an artefact of slight misalignment between the 'writing drive' and the 'reading drive'.The other possibility is it's down to the discs I'm using - mostly BBC Micro ones, likely written with 40/80tk "switchable" drives, which would all have had 80tk/96tpi/0.155mm heads.