PDA

View Full Version : Amiga HD drives



Dreamcast270mhz
June 21st, 2009, 07:17 PM
I've heard amiga HD drives work different from a PC HD drive, not just in filesystems, but in the way they write. For instance, if you got a catweasel and used your PC HD drive to write a HD image onto a floppy, the contents end in garbage. The same goes for a HD Amiga drive in a PC. So, what's the biggest difference, and do you think it would be possible to modify/hack a PC HD drive, creating millions of cheap amiga drives, that can write to an OFS floppy?

RetroHacker_
June 24th, 2009, 09:10 AM
The biggest difference is the actual rotation speed of the disk. You see, in a PC, the drive always spins at 300RPM, and the data rate simply doubles (from 250kbps to 500kbps IIRC) for high density. The Amiga, on the other hand, can't handle this higher data rate. So, to get around this, they simply halved spindle speed of the drive to run at 150RPM, and kept the data rate the same.

You can therefore use a PC drive in an Amiga as an 880k drive fairly easily, but using it as a high density drive won't work, since the PC drive can't go to that slower speed.

There are numerous hacks and kludges on Aminet for making it work, (overclocking the floppy controller, etc), but it will never be quite as reliable as the real thing.

I would have thought, however, that the Catweasel should be able to make disks that work in an Amiga. It's capable of the higher data transfer speed, and it's also capable of handling the GCR recording format that Amiga disks use.

-Ian

bear
June 24th, 2009, 01:35 PM
Even though the hardware is theoretically capable of dealing with it, the normal Amiga disk format is NOT GCR. It's MFM (just like a PC) but with 11 sectors per track instead of 9 (or 8), and a few other wrinkles thrown in to confound the PC floppy controller.

As it happens the Catweasel is SO flexible that it can be programmed to write variable-speed formats on fixed-speed drives (i.e. Macintosh 800k). In fact the Linux cwfloppy driver for Catweasel is already capable of reading and writing 1.7 MB Amiga floppies.

I suggest if the OP is having trouble writing Amiga HD format using Catweasel, he is not using software which has this capability. This highlights one of the perennial problems with the Catweasel, which is that the developers have largely failed to draw a distinction between what the hardware is capable of doing in theory, and what can be achieved using software which actually exists.

carlsson
June 24th, 2009, 11:40 PM
I thought the Amiga DD format used 80 tracks of one long sector each, and this sector is soft divided into 11 sectors. This would be opposed to a PC FDC which reads those 8-9 fixed sectors from each track.

RetroHacker_
June 25th, 2009, 04:25 AM
Even though the hardware is theoretically capable of dealing with it, the normal Amiga disk format is NOT GCR. It's MFM (just like a PC) but with 11 sectors per track instead of 9 (or 8), and a few other wrinkles thrown in to confound the PC floppy controller.

Ah, yes, now I remember. Heh. It's the Commodore 64 that used the GCR disk format.


This highlights one of the perennial problems with the Catweasel, which is that the developers have largely failed to draw a distinction between what the hardware is capable of doing in theory, and what can be achieved using software which actually exists.

And the entire reason why I didn't buy one when they first came out. The software was always "coming soon". That, and they never seemed to update their website, or be clear about how one would actually go about ordering the stupid thing.

But that was years ago. I know that since then, there is now working software for the Catweasel (written by other people), but I still don't think any of it has lived up to all the formats that the card is supposed to be able to handle. And, now, I'm still not sure how to buy one.

-Ian