Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!elroy.jpl.nasa.gov!ames!haven!umd5!hans
From: hans@umd5.umd.edu (Hans Breitenlohner)
Newsgroups: comp.sys.atari.8bit
Subject: Re: Flight Simulator II
Keywords: disk drive speed
Message-ID: <6475@umd5.umd.edu>
Date: 4 May 90 22:31:27 GMT
References: <9005030505.AA22343@Sunburn.Stanford.EDU> <1990May4.023039.11492@msuinfo.cl.msu.edu>
Reply-To: hans@umd5.umd.edu (Hans Breitenlohner)
Organization: University of Maryland, College Park
Lines: 38

In article <1990May4.023039.11492@msuinfo.cl.msu.edu> conklin@frith.uucp (Terry Conklin) writes:

>
>Anyone out there good with 6502 game to wander through the disk and pull
>the protection scheme?
>
>Terry Conklin
>uunet!frith!conklin
>conklin@egr.msu.edu
>The Club (517) 372-3131

If I had an XF551 and Flight Simulator (I have neither) I would try one
of the following:
 1. Permanently slow down the drive from 300 rpm to 288 rpm.  This should
    be close enough that things don't break too badly.  Or, if that does
    not work ...
 2. Install a switch to change drive speed on the fly.

Or, if somebody wants to donate an XF551 and Flight Simulator, I would love
to work on breaking the copy protection scheme!
Given the price of used 1050s and 810s I fear nobody will take me up on that
offer.

FS II uses a particularly nasty copy-protection scheme.  Normally each disk
track has sectors numbered 1-18.  On the FS II disk, there are sectors 1-16,
and two sectors numbered 17.  When you go to read that sector, it depends
on the timing (based on what sector you read last, and how long ago) which
of the two copies of sector 17 you get.
Some games do such things on one track, just to check the copy protection.
But FS II does so on every track, and they might even have valid stuff
in both sectors, picking what they get by what sector they read before.

This scheme is fragile, as it will fail, for instance, if the disk drive
retries the read because of an error.  And the fact that a change from
288 to 300 rpm broke it shows how little margin for error they left.

I guess all we can do at this point is to be sure to remember this
the next time we are tempted to buy a product from SubLogic.