5 ms·

What is the “two-drive trick” that can read Amiga disks on a PC?

151 points by _Microft 7y ago

mnw21cam 7y ago
Very clever. Presumably this would be unable to read high density (1.76MB) Amiga disks.
- elweston2 7y ago
  Would probably depend on the drive. There were utils out there in DOS land that let you format higher than normal. Usually by playing with the sector/track sizes. But it depended on the drive to let you do it. The best I ever got was ~1.6 out of my drives/media.
  - mnw21cam 7y ago
    The trick works by using the double sampling rate to inspect the normal data rate disk surface. When the disk surface already has a double data rate, the drive doesn't have a quadruple data rate mode to be able to read it.
- LIV2 7y ago
  Amiga HD floppy drives spun at 150RPM rather than the usual 300 from my understanding because the chipset couldn't handle a higher bitrate whereas on a PC the FDC switches between 250/500Kbit/s modes so I wonder if a pc controller could indeed read an Amiga HD floppy at all or if there are other differences?
- rasz 7y ago
  Commodore never upgraded Paula chip (knowing that company they probably immediately fired designer and didnt keep documentation to the chip), every model got the same 1985 state of the art Double Density floppy controller all the way to 1994 bankruptcy. As LIV2 already mentioned even their top of the line $3.5k A4000 Workstation shipped with gimped Floppy subsystem.
  - mnw21cam 7y ago
    The floppy drive could read/write high density 1.76MB disks. I know, I had one. You're right that the Paula chip wasn't upgraded to handle double the data rate from the drive. The solution instead was that the disk span at half the speed.
LIV2 7y ago
That's a really cool hack, I wonder if it would work on 82077AA or compatibles? I might give that a try later this month after I resurrect my A500 Presumably it should be possible to create a simple drive emulator to spit out that sector/track header without needing an actual disk. Not sure if I'm smart enough to tackle that but it's worth a try! I'm already working on a 6502 System at the moment that has an 82077AA compatible FDC and can read PC Formatted floppies so it should be relatively easy for me to tool around with this hack.
- jacobush 7y ago
  There are now quite a few floppy emulators of all kinds of flavors. One: https://github.com/keirf/FlashFloppy https://github.com/keirf/FlashFloppy
  - LIV2 7y ago
    Yeah, I've got a gotek for my A500 but I like to take on stupid useless projects, like a uC that does nothing except spit out sector headers lol
- deleted 7y ago
  [deleted]
_Microft 7y ago
Maybe I am a bit sentimental here but I found the low-level tinkering I did with computers during school much more interesting than the high-level things I learned to do later. Things like toggling the keyboards LEDs for the very first time felt just great. That reminds me how easy (QBasic!) it was to get started with it. I think it was the lack of abstraction and the verbosity and 'speaking' names of some statements (select case, goto) that made it so accessible for someone with no teacher and without any prior experience with programming. Even gotos themselves might have helped on that journey as they made the control flow much more comprehensible. Stuff happens in your program and IF you want it to happen again THEN GOTO the beginning. That it worked out of the box and didn't require any setup might have contributed as well.
- gdubs 7y ago
  Steve Woz talks about this in his autobiography. That basically, today’s generation is mostly missing an experience he was lucky to have: a complete understanding of a machine and all of its parts.
  - dragontamer 7y ago
    I respectfully disagree. Arduino can be fully understood from the ground up: from voltage-levels, to the clock, to the simple assembly language (and compiler). The AtMega328p is an incredibly simple design... rugged enough to withstand a variety of voltages (1.8V to 5V inputs), and even able to be used on a breadboard. Even ignoring Arduino, the "toy computers" that people make today are Minecraft Redstone, Factorio circuits, and Dwarf Fortress river-contraptions. Complete computer architectures built up from the fundamentals for the video-game computer scientists of the future. People play games and use toys because its possible to understand everything. EDIT: Oh, and the TI-83 calculator. Overpriced obsolete garbage of a calculator, but since its the "standard" calculator of High School, plenty of children will get the opportunity to really learn that machine if they so choose. There's something to be said about the TI-83 community keeping that Z80 chip so well documented and alive...
    - Sileni 7y ago
kstenerud 7y ago
I used this trick to back up my 5000 disk Amiga collection in the 90s. Bought a few extra floppy drives for $10 each at the local flea market :)
- rasz 7y ago
  According to the writeup this trick was invented in December 1999, was it known before?
  - kstenerud 7y ago
    It was definitely before 1997, because that's when I moved to Japan.
Pete_D 7y ago
Suppose someone still had a box or two of old Amiga floppies but no old hardware - what is the easiest way in 2019 to turn them into .adfs?
- tyingq 7y ago
  Not the easiest way, but interesting. http://amiga.robsmithdev.co.uk/history http://amiga.robsmithdev.co.uk/history
- snvzz 7y ago
  A few open solutions: http://amiga.robsmithdev.co.uk/ http://amiga.robsmithdev.co.uk/ https://github.com/jtsiomb/usbamigafloppy https://github.com/jtsiomb/usbamigafloppy http://cowlark.com/fluxengine/ http://cowlark.com/fluxengine/ And the kryoflux, which is proprietary but very good: https://webstore.kryoflux.com/catalog/index.php?cPath=1 https://webstore.kryoflux.com/catalog/index.php?cPath=1
- rasz 7y ago
  link is right there, under the post https://www.amigaforever.com/kb/13-118 https://www.amigaforever.com/kb/13-118 Easiest would be finding your local retro computer museum/club.
nullc 7y ago
Life, Uh, Finds a Way.gif

151 points by _Microft 7y ago

mnw21cam 7y ago

Very clever. Presumably this would be unable to read high density (1.76MB) Amiga disks.

elweston2 7y ago
Would probably depend on the drive. There were utils out there in DOS land that let you format higher than normal. Usually by playing with the sector/track sizes. But it depended on the drive to let you do it. The best I ever got was ~1.6 out of my drives/media.
- mnw21cam 7y ago
  The trick works by using the double sampling rate to inspect the normal data rate disk surface. When the disk surface already has a double data rate, the drive doesn't have a quadruple data rate mode to be able to read it.
LIV2 7y ago
Amiga HD floppy drives spun at 150RPM rather than the usual 300 from my understanding because the chipset couldn't handle a higher bitrate whereas on a PC the FDC switches between 250/500Kbit/s modes so I wonder if a pc controller could indeed read an Amiga HD floppy at all or if there are other differences?
rasz 7y ago
Commodore never upgraded Paula chip (knowing that company they probably immediately fired designer and didnt keep documentation to the chip), every model got the same 1985 state of the art Double Density floppy controller all the way to 1994 bankruptcy. As LIV2 already mentioned even their top of the line $3.5k A4000 Workstation shipped with gimped Floppy subsystem.
- mnw21cam 7y ago
  The floppy drive could read/write high density 1.76MB disks. I know, I had one. You're right that the Paula chip wasn't upgraded to handle double the data rate from the drive. The solution instead was that the disk span at half the speed.

LIV2 7y ago

That's a really cool hack, I wonder if it would work on 82077AA or compatibles? I might give that a try later this month after I resurrect my A500 Presumably it should be possible to create a simple drive emulator to spit out that sector/track header without needing an actual disk. Not sure if I'm smart enough to tackle that but it's worth a try! I'm already working on a 6502 System at the moment that has an 82077AA compatible FDC and can read PC Formatted floppies so it should be relatively easy for me to tool around with this hack.

jacobush 7y ago
There are now quite a few floppy emulators of all kinds of flavors. One: https://github.com/keirf/FlashFloppy https://github.com/keirf/FlashFloppy
- LIV2 7y ago
  Yeah, I've got a gotek for my A500 but I like to take on stupid useless projects, like a uC that does nothing except spit out sector headers lol
deleted 7y ago
[deleted]

_Microft 7y ago

Maybe I am a bit sentimental here but I found the low-level tinkering I did with computers during school much more interesting than the high-level things I learned to do later. Things like toggling the keyboards LEDs for the very first time felt just great. That reminds me how easy (QBasic!) it was to get started with it. I think it was the lack of abstraction and the verbosity and 'speaking' names of some statements (select case, goto) that made it so accessible for someone with no teacher and without any prior experience with programming. Even gotos themselves might have helped on that journey as they made the control flow much more comprehensible. Stuff happens in your program and IF you want it to happen again THEN GOTO the beginning. That it worked out of the box and didn't require any setup might have contributed as well.

gdubs 7y ago
Steve Woz talks about this in his autobiography. That basically, today’s generation is mostly missing an experience he was lucky to have: a complete understanding of a machine and all of its parts.
- dragontamer 7y ago
  I respectfully disagree. Arduino can be fully understood from the ground up: from voltage-levels, to the clock, to the simple assembly language (and compiler). The AtMega328p is an incredibly simple design... rugged enough to withstand a variety of voltages (1.8V to 5V inputs), and even able to be used on a breadboard. Even ignoring Arduino, the "toy computers" that people make today are Minecraft Redstone, Factorio circuits, and Dwarf Fortress river-contraptions. Complete computer architectures built up from the fundamentals for the video-game computer scientists of the future. People play games and use toys because its possible to understand everything. EDIT: Oh, and the TI-83 calculator. Overpriced obsolete garbage of a calculator, but since its the "standard" calculator of High School, plenty of children will get the opportunity to really learn that machine if they so choose. There's something to be said about the TI-83 community keeping that Z80 chip so well documented and alive...
  - Sileni 7y ago

kstenerud 7y ago

I used this trick to back up my 5000 disk Amiga collection in the 90s. Bought a few extra floppy drives for $10 each at the local flea market :)

rasz 7y ago
According to the writeup this trick was invented in December 1999, was it known before?
- kstenerud 7y ago
  It was definitely before 1997, because that's when I moved to Japan.

Pete_D 7y ago

Suppose someone still had a box or two of old Amiga floppies but no old hardware - what is the easiest way in 2019 to turn them into .adfs?

tyingq 7y ago
Not the easiest way, but interesting. http://amiga.robsmithdev.co.uk/history http://amiga.robsmithdev.co.uk/history
snvzz 7y ago
A few open solutions: http://amiga.robsmithdev.co.uk/ http://amiga.robsmithdev.co.uk/ https://github.com/jtsiomb/usbamigafloppy https://github.com/jtsiomb/usbamigafloppy http://cowlark.com/fluxengine/ http://cowlark.com/fluxengine/ And the kryoflux, which is proprietary but very good: https://webstore.kryoflux.com/catalog/index.php?cPath=1 https://webstore.kryoflux.com/catalog/index.php?cPath=1
rasz 7y ago
link is right there, under the post https://www.amigaforever.com/kb/13-118 https://www.amigaforever.com/kb/13-118 Easiest would be finding your local retro computer museum/club.

nullc 7y ago

Life, Uh, Finds a Way.gif