home *** CD-ROM | disk | FTP | other *** search
- Path: northshore.shore.net!not-for-mail
- From: farren@shore.net (Mike Farren)
- Newsgroups: comp.sys.amiga.hardware
- Subject: Re: Amiga disks with PC?
- Date: 11 Apr 1996 21:26:43 -0400
- Organization: Focus Studios
- Message-ID: <4kkbgj$llo@northshore.shore.net>
- References: <9604101952.AA00bb0@batesg.demon.co.uk>
- NNTP-Posting-Host: northshore.shore.net
- X-Newsreader: NN version 6.5.0 #19 (NOV)
-
- Gary Bates <gary@batesg.demon.co.uk> writes:
-
- >I am sure I'm right, but I want a more technical explanation by somebody
- >that knows a bit more about it than me.
-
- You're right, and here's why:
-
- First off - there is no difference whatsoever between an IBM PC floppy
- drive and an Amiga floppy drive (at least, not with the DD ones, and
- the difference between the HD drives is simply that the Amiga's has
- circuitry which allows it to spin at 1/2 speed). So as far as the
- drives are concerned, there is no reason you can't read an Amiga floppy
- with an IBM PC floppy drive.
-
- But the drives aren't the only thing that matters, here. All floppy
- disks run through a controller of one sort or another. On the Amiga,
- the "controller" is the custom chip Paula, but its functionality is
- very limited. All that Paula does is buffer the data coming from the
- floppy drive, allowing the CPU, by way of the trackdisk.device driver,
- to do all of the decoding, processing, and other operations on the
- floppy's data.
-
- An IBM PC's controller, though, doesn't work like this. They are,
- without an exception that I'm aware of, self-contained "computers"
- designed to work with a very specific set of parameters. In particular,
- all data decoding takes place internally to the controller, so you are
- limited to those schemes that the controller can handle.
-
- What this means in practical terms is simple. The Amiga's floppy disk
- format is unique to the Amiga. The layout of a track on an Amiga
- floppy involves a very particular and unusual MFM encoding scheme,
- along with continuous data - the sectors aren't separated from one
- another in any way. An IBM PC's floppy controller chip simply can't
- handle this; it expects to see a layout which includes sector headers,
- intersector gaps, and a very specific method of MFM encoding for the
- data for each of those things. While they're programmable within
- limits (you can, for example, specify the sector size), the limits do
- not include the ability to read the raw data from the disk and
- translate it into "real" data by doing the custom MFM decoding that the
- Amiga does. There is no way at all for a PC to bypass the floppy
- controller chip, it's simply not possible. If there were a way to read
- the raw floppy data, this would be possible; but there's not.
-
- --
- Michael J. Farren, Ex-Lemmings Manager | All standard disclaimers apply.
- Currently unemployed - know anyone |
- looking for a good game programmer? | Are we not Lemmings? If you click
- farren@shore.net, farren@well.com | us, do we not ... Oh, no!
-