8 ms·

Amiga had floppy drives that could read/write 1.76MB on HD disks and 880K on SD floppys. I think this was possible because they could control the speed.

basementcat 3y ago
Mac drives had finer control over the motor RPM. Amiga drives read/wrote a track at a time and had no sector gaps. https://porterolsen.wordpress.com/2016/06/15/accessing-mac-formatted-floppy-disks-without-the-kryoflux/ https://porterolsen.wordpress.com/2016/06/15/accessing-mac-f... https://c65gs.blogspot.com/2023/10/reading-amiga-disks-in-mega65.html?m=1#:~:text=The%20following%20are%20details%20about,No%20gaps%20written%20between%20sectors https://c65gs.blogspot.com/2023/10/reading-amiga-disks-in-me....
rasz 3y ago
The only HD drive ever available for Amiga was sold with some 4000 units - a modded Chinon FZ357A spinning at half rpm because nobody at commodore knew how to update PLL circuit in Denise. 1.76MB capacity was reached by not using standard PC format. Microsoft itself was shipping software on ordinary PC floppies formatted for 1.68MB https://en.wikipedia.org/wiki/Distribution_Media_Format https://en.wikipedia.org/wiki/Distribution_Media_Format
- Cockbrand 3y ago
  My A3000 has an HD floppy drive. I was surprised to find that out, as I hadn't been aware that Amigas with these drives existed.
- snvzz 3y ago
  Not Denise, Paula. Denise is the video chip. Paula handles interrupts, audio, the floppy data signal (control logic signals are in CIA) as well as the uart.
  - bcrl 3y ago
    Paula being the only chip that had absolutely zero changes from the Amiga 1000 to the 4000. That fact alone is a sad example of Commodore's mismanagement of the platform. Well, except for the CIA which traces its lineage even further back to the C64.
    - snvzz 3y ago
      Try Commodore The Inside Story (book) for more depressing knowledge. Management just didn't let their engineers/architects get things done.
snvzz 3y ago
This was due to different track format. 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.
- skissane 3y ago
  > 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.
  - 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.
JNRowe 3y ago
Thanks to the pluggable device layer, you could push that to 984kB or 1968kB with diskspare¹. The incredible thing, IMO, is that the implementation is only 5kB(seven times smaller than the formatted English docs). ¹ https://aminet.net/package/disk/misc/Diskspr3 https://aminet.net/package/disk/misc/Diskspr3

basementcat 3y ago

Mac drives had finer control over the motor RPM. Amiga drives read/wrote a track at a time and had no sector gaps. https://porterolsen.wordpress.com/2016/06/15/accessing-mac-formatted-floppy-disks-without-the-kryoflux/ https://porterolsen.wordpress.com/2016/06/15/accessing-mac-f... https://c65gs.blogspot.com/2023/10/reading-amiga-disks-in-mega65.html?m=1#:~:text=The%20following%20are%20details%20about,No%20gaps%20written%20between%20sectors https://c65gs.blogspot.com/2023/10/reading-amiga-disks-in-me....

rasz 3y ago

The only HD drive ever available for Amiga was sold with some 4000 units - a modded Chinon FZ357A spinning at half rpm because nobody at commodore knew how to update PLL circuit in Denise. 1.76MB capacity was reached by not using standard PC format. Microsoft itself was shipping software on ordinary PC floppies formatted for 1.68MB https://en.wikipedia.org/wiki/Distribution_Media_Format https://en.wikipedia.org/wiki/Distribution_Media_Format

Cockbrand 3y ago
My A3000 has an HD floppy drive. I was surprised to find that out, as I hadn't been aware that Amigas with these drives existed.
snvzz 3y ago
Not Denise, Paula. Denise is the video chip. Paula handles interrupts, audio, the floppy data signal (control logic signals are in CIA) as well as the uart.
- bcrl 3y ago
  Paula being the only chip that had absolutely zero changes from the Amiga 1000 to the 4000. That fact alone is a sad example of Commodore's mismanagement of the platform. Well, except for the CIA which traces its lineage even further back to the C64.
  - snvzz 3y ago
    Try Commodore The Inside Story (book) for more depressing knowledge. Management just didn't let their engineers/architects get things done.

snvzz 3y ago

This was due to different track format. 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.

skissane 3y ago
> 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.
- 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.

JNRowe 3y ago

Thanks to the pluggable device layer, you could push that to 984kB or 1968kB with diskspare¹. The incredible thing, IMO, is that the implementation is only 5kB(seven times smaller than the formatted English docs). ¹ https://aminet.net/package/disk/misc/Diskspr3 https://aminet.net/package/disk/misc/Diskspr3