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View Full Version : What disk formats can the 1571 and 1581 be coerced into reading?



gsteemso
June 18th, 2009, 04:56 AM
For background on why I'm asking about this, see my post here (http://vintage-computer.com/vcforum/showthread.php?t=16107) in the Early Apple subforum on this site. A quick summary: I have, in addition to my Commodore stuff, some Apple II and Mac stuff. The more recent Macs have internet connectivity, and they all have floppy drives of various types. This leads naturally to a process of floppy disk transfers that will get vintage disk images hot off the 'net onto real floppies for use on real hardware.

So, for starters, can the 1581 be made to read an Apple II 800K disk? As far as I can determine from extensive Googling, Apple 800K disks (which are magnetically the same whether for Apple II or for Mac, though the file systems vary drastically) use both GCR encoding and variable rotation speed, which is why they can't be read in a standard PC drive (MFM encoding and fixed 300 RPM speed). Do I understand correctly that the 1581 encodes in MFM? It doesn't seem to say online anywhere.

Given that the DIY 1581s Joe Palumbo sells need a standard PC floppy drive of a specific brand to be completed, things look iffy for cross-platform compatibility. Still, the 1581 must do SOMETHING different a PC only gets 720K onto one of those floppies, but the 1581 attains 800K without difficulty.

If the 3.5" thing doesn't pan out, there's always 5" disks. Both Apple II and Commodore disks use GCR encoding on a 35-of-40-track format. Do they use the same GCR scheme? How about the number of sectors per track? At least the 1571 format is well documented. Does anyone know of a reason the 1571 can't be made to read an Apple II floppy?

carlsson
June 18th, 2009, 07:29 AM
Yes, I believe the 1581 uses MFM encoding. There are some software that will let you read and even write such floppies on a standard PC, although some FDC's are more capable of being reprogrammed than others. The DIY kits actually are real 1581's minus the mechanism. I don't know how picky they are, just that you need access to a couple of jumpers and perhaps some RDY signal.

It appears there are DOS extentions that let you record more than 720K on a PC floppy too. However without the extention those floppies would be gibberish.

Raven
June 23rd, 2009, 11:43 PM
I know this bypasses the fun, techie side of your project, but you can just buy an adapter to hook the 1571 or other C64 drive to a PC (or probably anything else with a parallel port and a driver), and write the images that way. This is what I do (works great!).

carlsson
June 24th, 2009, 01:54 AM
He almost exclusively mentioned classic Macs and 8-bit Apples though. I may be wrong, but they generally don't have traditional parallel ports onboard. At least I'm not aware of any Mac version of the X-series or such software.

If the Mac is modern enough, you could run VirtualPC and have an USB to LPT adapter, which reportedly will work. See this mailing list archive from 2003:

http://www.softwolves.pp.se/misc/arkiv/cbm-hackers/8/8443.html