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True, they use these pre-existing standard controllers. But these standard controllers and the track format were indeed designed in that way due to the ram limi

by snvzz 3y ago

True, they use these pre-existing standard controllers. But these standard controllers and the track format were indeed designed in that way due to the ram limitation. Ironically, it is possible to read arbitrary formats with the debug read track operation. Yet, it needs to find one triple sync word somewhere in the track; a controller limitation. Unfortunately, the Amiga standard track format didn't account for that, and uses the same sync word (the 4489 one) but double. It could have been designed to use a different sync word, and include a triple 4489 at the track start, but they didn't think about it at the time. Some tricks bit-banging the controller allow for writing arbitrary tracks. It is also possible to read arbitrary tracks, if there's two floppy drives and a standard ibm pc formatted disk is present in the other one, by switching the drive after the controller has started reading.

skissane 3y ago
> But these standard controllers and the track format were indeed designed in that way due to the ram limitation. The track format was designed that way in the early 1970s. RAM was likely one reason for it, but another was that the 3740 used sector gaps as record boundaries; it was commonly configured so each 128 byte disk sector held a single 80-column punch card worth of data. 3740 format floppies support deleting sectors (by using a different sync word in the sector header) so you could delete database records. PC floppy controllers supported deleted sectors too, even though almost no software used them (some copy protection schemes did, but duplicating deleted sectors isn’t hard once you know they exist.) Part of the motivation for 128 byte sectors was likely the fact that it was the smallest power of 2 that could fit a whole punch card. Also, a whole 3740 track was 3338 bytes (26 sectors of 128 bytes), which was a lot of RAM in 1973; in 1981, a whole PC floppy track was 4096 bytes. 4KB was a lot less expensive in 1981 than in 1973, so by then it would have been less of a motivating factor than when the track format was initially defined.

by snvzz 3y ago

skissane 3y ago

> But these standard controllers and the track format were indeed designed in that way due to the ram limitation. The track format was designed that way in the early 1970s. RAM was likely one reason for it, but another was that the 3740 used sector gaps as record boundaries; it was commonly configured so each 128 byte disk sector held a single 80-column punch card worth of data. 3740 format floppies support deleting sectors (by using a different sync word in the sector header) so you could delete database records. PC floppy controllers supported deleted sectors too, even though almost no software used them (some copy protection schemes did, but duplicating deleted sectors isn’t hard once you know they exist.) Part of the motivation for 128 byte sectors was likely the fact that it was the smallest power of 2 that could fit a whole punch card. Also, a whole 3740 track was 3338 bytes (26 sectors of 128 bytes), which was a lot of RAM in 1973; in 1981, a whole PC floppy track was 4096 bytes. 4KB was a lot less expensive in 1981 than in 1973, so by then it would have been less of a motivating factor than when the track format was initially defined.