Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!apple!oliveb!sun!pepper!cmcmanis
From: cmcmanis%pepper@Sun.COM (Chuck McManis)
Newsgroups: comp.sys.amiga
Subject: Re: Getting 1.5 MB on a standard 880K floppy without compression
Keywords: Roomers
Message-ID: <94323@sun.Eng.Sun.COM>
Date: 16 Mar 89 18:16:15 GMT
References: <3631@sugar.hackercorp.com>
Sender: news@sun.Eng.Sun.COM
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 22

In article <3631@sugar.hackercorp.com> (Karl Lehenbauer) writes:
>In the Roomers column of the March 1989 issue of Amazing Computing, the
>Bandito says that certain game companies are getting 1.5 MB unformatted
>on standard 880K floppies.
>Can anyone verify if this is true and if so, explain how it works?

If we consider that the "traditional" unformatted capacity of the 
standard 3.5" disk is 1MB, it would seem they were getting an exact
50% increase in space. And that would suggest that they had rewritten
trackdisk.device to use RLL encoding rather than MFM encoding. This
is entirely possible, unfortunately I can't think of any way right
off hand you could decode the RLL bits with the blitter. This may be
good or bad depending on how you look at it. It's good because the 
decoded buffer doesn't have to be in chip ram, it's bad because the
CPU is doing all of the decoding and that could impact your floppy
transfer rate. Check out the Western Digital Disk Controller Handbook
for a description of how the bits lay in RLL mode.


--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.