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From: cc@rayssd.RAY.COM (Charles R Coday)
Newsgroups: comp.sys.atari.8bit
Subject: Re: questions
Message-ID: <442@rayssd.RAY.COM>
Date: Sat, 6-Dec-86 13:47:35 EST
Article-I.D.: rayssd.442
Posted: Sat Dec  6 13:47:35 1986
Date-Received: Sun, 7-Dec-86 04:02:57 EST
References: <7117@topaz.RUTGERS.EDU> <468@inuxm.UUCP> <434@rayssd.RAY.COM> <1385@umd5>
Sender: cc@rayssd.RAY.COM (Charles R Coday @ Raytheon Company, Portsmouth RI)
Distribution: net
Organization: Raytheon Company, Portsmouth RI
Lines: 30
Summary: Re: Re: questions

In article <1385@umd5>, hans@umd5 (Hans Breitenlohner) writes:
> In article <434@rayssd.RAY.COM> cc@rayssd.RAY.COM (Charles R Coday) writes:
> >
> >	I have used Dos 2.0 (unmodified) with double density drives thru
> >an ATR8000 in the double density mode.  Most of the double density drives
> >and their mods will automatically switch to the correct density upon
> >boot-up.  Atari Dos 2.0 gets notified of the appropriate density and then
> 
> I don't think you are quite right about this.  There is no code in Dos 2.0
> to treat the first three sectors of the disk specially (i.e. 128 instead of
> 256 bytes), so any function which writes these (format, write Dos files, etc.)
> will fail.  Perhaps the ATR 8000 compensates for this, and allows you to write
> these sectors either way, but I am sure a regular disk drive will not do this.

What I failed to include was the information that the first three sectors
must be 128 bytes ONLY regardless of their density AND the drive MUST
switch densities by itself (yes--the ATR8000 does the 'switching').  This
concept was first implemented by PERCOM who used to make drives for many of
the home micros, including ATARI.  When Rana came on the scene they
implemented the same idea ( I also had one of those at one time).  The real
proof, of course, is to insert a double density disk and see what happens. 
The various DOSes like MYDOS, SMARTDOS, etc have the capability to create a
double-density disk with a DOS on it.  DOS 2.0, tho, won't do that. 

So how can you get a double-density disk with DOS 2.0?

I did it in the past with a PD program circulated by PERCOM, but they went
out of the ATARI drive business.  BUT, if someone really wants a
double-density DOS 2.0, I will try to find the program and post it (if I
can figure out how to do that!).