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From: Ari Lukumies <nospam DOT ari DOT lukumies AT gmail DOT com DOT invalid>
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Subject: Re: Creating a copy protected floppy
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Date: Thu, 14 Jul 2005 19:45:07 +0300
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To: djgpp AT delorie DOT com
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Hello wrote:
> There are a
> wide variety of controllers, and not all of them handle 'non standard' disks
> well.
> 
> As an example, even when the floppy is formatted properly (according to the
> ibm floppy specs), some floppies can still have problems.  This is why the
> PC can have so much trouble reading some floppies of old 8 bit micro's back
> from the 80's.

IMNSHO, this is more caused by the drive's rw-heads capabilities and 
speed tolerances. When you format a disk on an in-tolerance drive 
(say, its head min positioned, but in tolerance), and try to read it 
in another in-tolerance drive (say, its head max positioned, but still 
in tolerance), the disk can usually not be read. (The tolerance, if 
memory serves, was -4% to +4%, but that would need a rw-head that 
could fill the whole 8% width.) Same goes for the rotating speed, 
although the percentages probably were different.

Later, IBM introduced the 1.2MB floppy disk. It had even more 
problems, since it used narrower rw-heads than the previous 360kB 
drives (due to the need to squeeze more tracks on the surface of the 
same size). This usually meant that if you formatted a 360kB disk in a 
1.2MB drive, the disk was not readable in a 360kB drive, since the 
positioning of the heads (and the narrower "format beam", so to say, 
used in formatting) did not meet.

BTW, this goes for hard disks, also: if you use one in one computer 
and move it to another, it may require reformatting before being 
usable (or reliably stabile, at least).

> Even if those use the official format, the typical PC controller can be
> picky enough to make it difficult to read.  Very often the problems are a
> slight differences in rotation speed between the original and the pc, and a
> gap after the index hole that's too short.

The gap lengths can be reprogrammed. And the sector interleaving (the 
sectors need not be contiguous, in most cases, interleaving makes the 
disk faster to access).

> There are lots of programs still around that copy disks by doing full track
> copies, rather than sector by sector.

The question probably is, do they scan each track before the copying 
process (for example, you can have different number and length of 
sectors on each track, as far as the NHCR fields are valid).

> Most of those prorgrams are back from the dos days in the mid 80's, when
> copy protected disks were so common.
> But they still work with today's hardware.

Not necessarily. A program called CopyIIPC, for example, refuses to 
work with modern PCs, since it uses the CPU speed for timing purposes. 
Using a 'slow-down' program doesn't help, because this copier doesn't 
tolerate change-of-speed-of-CPU during operation (which is caused by a 
slow-down prog).

> If somebody did want to copy a disk like that [copy-protected by one
 > of the ways mentioned], they could probably do a
> google search and find a suitable program within 10 minutes.
> 
> And once it's done, then the protection is cracked for good.  Anybody and
> everybody can do it themselves or use a patch or disk image, etc.

The OP didn't ask for an uncrackable solution - just for one that 
would fool a generic user (read: a modern 
windows-gui-and-mouse-is-all-there-has-ever-been user).

> In the old days, you could expect many people to not know about stuff like 
> that.  Not today.  Today, if somebody has a problem, then 30 seconds of 
> googling is all it takes.

How many of those "generic" users do you think knows the search words 
to use in looking for that problem in a google search?

> Floppy protection just doesn't work.  They are a pain in the ass, and there
> are so many programs to copy those supposedly uncopyable disks that it just
> isn't worth the time or trouble.

Some might find it an intereseting enough subject in researching 
something else (for example, the inner workings of the support chips 
inside a PC).

-atl-
-- 
A multiverse is figments of its own creations