This explains the 2M utility that allowed storing about 1.8mb on a floppy disk. It was fun playing with it.
This bit is particularly relevant: https://www.pagetable.com/docs/visualize_1541/sector.png See the solid bit at the end of the sector, just before the next header? You could squeeze a few more bytes in there, but if the drive motor is just slightly too fast, it'll overwrite the next sector. That's why there's a gap, tolerance for timing variation.
Most floppy drive technologies wrote blindly, guessing where they were on the disk based on timing estimates since the controller last saw a sector header. This is also why disks needed to be "formatted". Not just in the sense of writing the file system data structures, but writing out all the sector headers. This had to be done all at once with the same drive, due to those small timing variations.
https://porterolsen.wordpress.com/2016/06/15/accessing-mac-f... https://c65gs.blogspot.com/2023/10/reading-amiga-disks-in-me....
Microsoft itself was shipping software on ordinary PC floppies formatted for 1.68MB https://en.wikipedia.org/wiki/Distribution_Media_Format
Denise is the video chip. Paula handles interrupts, audio, the floppy data signal (control logic signals are in CIA) as well as the uart.
Management just didn't let their engineers/architects get things done.
Specifically, AmigaOS's floppies write one sector after another, with a single gap in the entire track.
Whereas the IBM PC format has a gap in each sector. This is because RAM was more expensive back then, thus holding an entire track in memory would have an associated cost.
A major factor - I'd argue even more significant than cost of memory - was that the IBM PC used an off-the-shelf floppy disk controller chip (NEC uPDC765A), which was hardwired to support the industry-standard IBM floppy track format (which had evolved from IBM's 3740 mainframe data entry system, introduced in 1973), and didn't support the Amiga's custom track format. Whereas, the Amiga could do this because it didn't actually have a floppy disk controller-the functionality of controlling floppy disks was in part contained in their custom ASICs, and in part implemented in software by the CPU. Unlike the Amiga, the original IBM PC eschewed proprietary ASICs in favour of off-the-shelf chips, in order to minimise time-to-market.
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.
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.
Then there were things like Spiradisc (https://en.wikipedia.org/wiki/Spiradisc), which created incompatibilities by design.
I guess the alignment on that one particular drive must have been ridiculously far off baseline.
Just the absolute worst drives ever released to the public, but it was that or tapes and while most will agree that the 1541 was a slow FDD, waiting 30+ mins to load a tape (don't forget to flip it) was much worse.
Then copy protection companies decided that the very best way to CP software was to create unreadable/unwritable sectors and let the drive slam the head against the arrester trying to read it, because they didn't have to replace the drive. That was a you problem.
The motors in the disk drives could be controlled directly, and you could pack the tracks tighter by stepping the motor just a little bit less than you were supposed to. And in theory if you did it right, other disk drives could read it.
'In theory' is carrying a lot there. I tended to find 1.5something to 1.6something worked and anything higher rarely ever did.
"There are 80 tracks on your average 3.5" floppy drive. You can select a given track by pulsing the STEP pin and combining it with the direction select pin."
The first few generations of consumer hard drives adopted some of these same techniques.
It was extra sectors not tracks, although is looks like some people added another track or three at the edge of the disk.
Writing the 1 depends on the precision of the magnets and I suspect they just weren't able to utilize the media better, with the tech of the time.
Now we use lasers. ;)
For real! Do they mean 2MB or 2Mb ?
https://m.youtube.com/watch?v=qSehRwClXNk
Tldr, a bit more than 1.7MB.