Amiga 5.25-inch floppy disks and drives

[mark_k]

As far as the Amiga was concerned, there were (at least) two different types of 5.25" floppy drive.

Commodore's own A1020 is a 40-track drive which can be used to access PC-format 160/180/320/360KB disks. It reports the correct 5.25" drive ID to trackdisk.device, so trackdisk knows to use different head step timings. 5.25" drives, at least 40-track ones, need slower head step timings than normal 3.5" drives.

In addition to using CrossDOS or the old PC Copy utility on the Extras disk to read/write PC disks, you can use a mount file to read/write 5.25" disks using trackdisk.device, 440KB on each disk. You can also use an A1020 to read Atari 8-bit, Apple II and C64 disks. (In order to read all speed zones of C64 disks you need to adjust the drive speed slightly. But after doing that, reading C64 disks in an A1020 is massively faster than using a real 1541.)

Since the A1020 is a real 40-track drive, there would be no interchange problems with transferring data from Amiga to Atari or Apple II. However I don't think anyone ever wrote an Amiga program to write Apple II-format disks.

Most third-party 5.25" drives are different. They use 80-track drive mechanisms and don't report the drive ID as a 5.25" drive, so as far as the Amiga is concerned the drive is the same as a normal 3.5" one. So trackdisk.device automatically "sees" the drive and you can format disks to 880KB. (I'm not sure whether the head step delay for 80-track 5.25" drives needs to be longer than for 3.5" ones.)

Software like CrossDOS has an option to double-step the drive heads, so it's possible to read 40-track PC disks in an 80-track drive.

Some third-party drives also have a 40/80 switch. In "40" mode the drive steps its heads twice each time the Amiga tells it to move the heads. The drive heads are still the narrower 80-track width, so writing disks for reading later in a 40-track drive (e.g. PC or Atari 8-bit) doesn't work reliably.

5.25" high density drives/disks aren't usable on the Amiga.

[mips]

Originally Posted by mark_k

Some third-party drives also have a 40/80 switch.

Now that you mention it I think my drive had a 40/80 track switch at the back. It spent most of it's life in the 80 position.

[prowler]

Originally Posted by mark_k

As far as the Amiga was concerned, there were (at least) two different types of 5.25" floppy drive.

Commodore's own A1020 is a 40-track drive which can be used to access PC-format 160/180/320/360KB disks. It reports the correct 5.25" drive ID to trackdisk.device, so trackdisk knows to use different head step timings. 5.25" drives, at least 40-track ones, need slower head step timings than normal 3.5" drives.

In addition to using CrossDOS or the old PC Copy utility on the Extras disk to read/write PC disks, you can use a mount file to read/write 5.25" disks using trackdisk.device, 440KB on each disk.

Most third-party 5.25" drives are different. They use 80-track drive mechanisms and don't report the drive ID as a 5.25" drive, so as far as the Amiga is concerned the drive is the same as a normal 3.5" one. So trackdisk.device automatically "sees" the drive and you can format disks to 880KB. (I'm not sure whether the head step delay for 80-track 5.25" drives needs to be longer than for 3.5" ones.)

Software like CrossDOS has an option to double-step the drive heads, so it's possible to read 40-track PC disks in an 80-track drive.

Some third-party drives also have a 40/80 switch. In "40" mode the drive steps its heads twice each time the Amiga tells it to move the heads. The drive heads are still the narrower 80-track width, so writing disks for reading later in a 40-track drive (e.g. PC or Atari 8-bit) doesn't work reliably.

5.25" high density drives/disks aren't usable on the Amiga.

Thanks for those details, Mark!

I have encountered 5¼-inch AmigaDOS disks formatted to 880kB, but was able to read them using a PC-compatible high density drive fitted to my Catweasel MkIV.

Now I can fully understand how they were written.

[TjLaZer]

Never heard of an 80 track 5.25" drive on the amiga in all my years messing with them!

[Jope]

They were moderately popular here in Europe. The two we got here in Finland were the Roctec RF542C and another was called the Master-5A.

http://amiga.unikko.org/C-lehti/jpeg/1989/5/07.jpg

They claim that the Master-5A was capable of diskchange detection, but I've never seen one in real life. I have the RF542C myself, which they said would need manual diskchange commands, but at least my unit does detect diskchanges just like a 3.5" drive would.

.. and I actually just cracked it open a moment ago. The drive mechanism has been built to support disk changes from the factory. There is an opto fork to detect a disk's presence and a microswitch that detects whether the door is closed. Seems it will be quite difficult to source a replacement if that mechanism ever dies. :-D

[Jope]

Based on a recent discussion in PM, I took a picture of the DIP switches of the RocTec RF-542C.

They're rather ambiguous, by the looks of things dip 3 and 4 need to be turned simultaneously.

http://jope.fi/amiga/rf542c.jpg