Path: utzoo!attcan!uunet!cs.utexas.edu!usc!samsung!munnari.oz.au!murtoa.cs.mu.oz.au!ditmela!latcs1!stephens
From: stephens@latcs1.oz.au (Philip J Stephens)
Newsgroups: comp.sys.apple2
Subject: Re: Disk timing
Message-ID: <7447@latcs1.oz.au>
Date: 19 Mar 90 13:47:10 GMT
References: <1848@crash.cts.com> <18491@boulder.Colorado.EDU> <429@helens.Stanford.EDU>
Organization: Comp Sci, La Trobe Uni, Australia
Lines: 42

In article <429@helens.Stanford.EDU>, joe@hanauma.stanford.edu (Joe Dellinger) writes:
> 
> Yes. The timing was so critical, in fact, that the position of some of DOS's
> code relative to page boundaries MATTERED, because of the 1-cycle timing
> difference that could make for some 6502 commands. Because of this, there
> were some "holes" scattered through DOS 3.3 so that the critical hunks of
> code would be properly aligned!

  Yeap, writing disk routines for the good ol' 5 1/4 inch drives is fun.
Understanding how the bugger works is even more fun.  I consider my biggest
achievement so far on my humble Apple ][+ was being able to disassemble the raw
code from the RWTS and finally (after many, many hours) _actually_
understanding what on earth it was doing!  No mean feat, I can tell you,
considering I had no idea what the I/O soft switches were used for, or what
the encoding scheme was, or the fact the drive arm used a stepper motor with
four phases...
  Come to think of it, I must have been mad... ;-)

> (PS: My Apple is so old that Prodos won't even boot on it. Anybody know why?
> Doesn't matter to me, I keep my old Apple for its antique value these days.
> It's a ][, not even a ][+ ...)

  Wow!  An Apple ][!  That certainly would be worth a bit nowdays, wouldn't
it?
  Has it got a 16K language card?  Because if not, that would be the prime
candidate for Prodos not booting (considering it resides underneath the ROM!).
If it's got less than 48K, then that's another reason why it won't boot, since
it needs the address space from $BF00-$BFFF.  In fact, if you've got less than
48K, then only an original DOS 3.3 master disk (or it's slaves) will boot on
a ][!
  Not only that, an Apple ][ wouldn't even be self booting, would it?  Doesn't
it just crash into the monitor when you turn it on?  I remember we had such
a beast (probably not a ][ though) at High School many years back.
  I suppose your ][ doesn't even have AppleSoft in the ROM's?  Or lowercase?
Only 2 colours (excluding black and white) in Hires?  How much will you sell
it for... :-)  

</\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\></\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\>
<  Philip J. Stephens                ><   "Many views yield the truth."        >
<  Hons. student, Computer Science   ><   "Therefore, be not alone."           >
<  La Trobe University, Melbourne    ><          - Prime Song of the viggies   >
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