
If you have Prince of Persia on 5.25", trade in for a 3.5". This is (or at least used to be) free. The 3.5" version is easy to deprotect:
 
Prince of Persia 3.5" deprotect:
 
Block: 7
Byte: $16
From: $90 (bcc)
To: $80 (bra)
 
Block: $A
Byte: $8C
From: $18 (clc)
To: $38 (sec)
 
This is to be used for archival purposes only.
 
It'll work from a 800K RAMdisk with this deprotect. Probably also a 800K HD
partition.
 
Jay, krell@cornell.edu




I don't question the availability for a crack, but, I do question Br0derbund's
usage of a quarter track in Prince of Persia.  I, too, received the program as a
gift (I still fell that it kills IBM P.O.P.(not 2) w/o a SoundBlaster) and I
immediately set out to make my legal backup.

At least in version 1.0 (press CTRL-V during game play to check)
there _IS NO_ quarter-track.  You can tell
quarter-tracks with true Apple Disk II drives.  You can hear a slight tick
instead of the chkkkkk....chkkkk....chkkkk normally heard when accessing
track-to-track.  I know this for a fact since this is how I detected the quarter
track in AirHeart at 1B.25!  In version 1.1 of P.O.P. there is the standard
Br0derbund 'A5 96 BF' header and pitfully-easy-to-crack bitslip protection.

Avoid the bit-slip routine by searching track #$00 on the boot side for E7 E7 E7.
I used Copy II+ (yes, a legal copy!) for any backing up.  Using a nibble editor
replace the seventh occurrence of the E7 pattern with AF F3 FC EE E7 FC EE E7 FC
EE EE FC.  This routine will cooperate with //c's and IIgs' unlike the PARM in
Copy II+ Plus designed to backup CrossWord Magic (backups won't boot except on 
//e's because of machine specific timings).

Anyway .. .. .. that is the copy protection which exists on
Prince of Persia.  This same scheme occurs on Tetris
from Spectrum Holobyte and Wings of Fury.  Epyx also used the bit-slip timing in
RoboCop, Ikari Warriors, California Games, World Games, Sub Battle Sim...
etc...Br0derbund used it on Carmen Sandiego's (not W.I.T.W), Type!, and Animate.
It was more fun to purchase the software just to crack it!

Let me know if stand corrected about Prince of Persia's copy-protection.


Michael Kelsey
mkelsey@eecs.wsu.edu

