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"Math Blaster" and "Ultima IV" share the same copy protection.
"Elite" and "Ernie's Quiz" share the same copy protection.
"Prince of Persia" has three separate E7 checks, but they all check the same bitstream in track 0 and can be defeated with a 12-byte patch.
Later Davidson & Associates disks can be identified by a single corrupted sector on track $22 whose data checksum is $3F instead of 0.
Once a floppy drive's motor is off, it always returns the same invalid value. Lady Tut polls it while off and reboots if the value changes!
If "Transylvania" fails its protection check, it deletes a vital location from the map and the game is unwinnable.
Activision games derive a magic value from the protection check and use it to calculate disk read parameters. The magic value is always $55.
To protect against memory capture cards, "Burgertime" checksums all peripherals during boot, then again in-game, and reboots on a mismatch.
"Spell It!" and "Autoduel" share the same copy protection.
"Impossible Mission II" has an encrypted bootloader. The 64-bit decryption key is part of the uncopyable E7 bitstream on track 0.
ProDOS-based Sunburst disks cycle through 4 RWTS variants on boot until one works. Each variant requires a different pattern of timing bits.
"Wavy Navy" tries to determine if ROM is writeable, to out-fake hardware modifications that lie about whether ROM or RAM is active at $F800.
"Spy's Demise" uses the disk volume number to initialize an unrelated (but critical) index variable in its disk read (POSTNIBBLE) routine.
"County Fair" RWTS ignores the RWTS parameter table, loads one sector that overwrites the caller in memory, and returns to a new bootloader.
The disk format of "Karateka" is so complicated that Copy II Plus added Karateka-only code to parse it.
Karateka's disk read routine intentionally crosses a page boundary, thus requiring every 256th nibble on disk to have an extra bit after it!
Karateka for iOS ships with an Apple II emulator and a cracked copy of the original disk because no emulator can handle the copy protection.
If "Tycoon" fails its protection check, it will overwrite the boot sector with garbage, rendering the disk unbootable.
After a game ends, "Beer Run" does a pointless JSR $0578 (part of the text screen) to an "RTS" instruction left in memory by the bootloader.
Sector 0 of "Mr. Do" contains a message from the protection developer, Jim Ratcliff: DON'T WASTE YOUR TIME, ORIGINALS ARE INEXPENSIVE.JCR
Sector 0 of my "Mr. Do" crack contains a response: TIME SPENT IN THE SERVICE OF HISTORY IS NEVER WASTED.4AM
"Match It!" DOS redefines INIT as a no-op, then calls it on launch. Booting from another disk and launching the game will format your disk.
"Deathsword" and "Audubon Grizzly Bears: Wildlife Adventures" share the same copy protection.
If "Computer Discovery" fails its protection check, it prints "ERROR CODE 593 -- CALL SRA FOR ASSISTANCE". Pro-tip: do not actually do that.
"Microzine 1" used a 34-bit address prologue -- 4 nibbles and 2 unusually placed timing bits -- that made it impervious to bit copiers.
Up'N Down sector 1: HELLO THERE THIS IS THE CREATOR OF U&D. THIS SECTOR ON THE DISK IS OF NO VALUE AND THERE IS NO SENSE EVEN LOOKING AT IT.
"Classifying Animals with Backbones" DOS decrypts BASIC programs on the fly. Booting another disk and LOADing them will lock up your Apple.
"Spanish Grammar Review" contains a track specifically designed to trigger a bad code path in the timing bit detection routine of Copy II+.
"The Observatory" has 6 wildly different disk read routines. One of them reads one sector each from 32 consecutive half tracks (not a typo).
If "Weather Forecasting" fails its protection check, it says "You are experiencing operating difficulty" in a nice hi-res graphical font.
"Gulp and Frenzy" pre-checks if its copy protection would fail on an original, says THE DRIVE YOU ARE USING IS OPERATING AT AN UNSAFE SPEED
"Video Title Shop" and "Tomahawk" share the same copy protection.
If you modify the self-decrypting protection check in "BC's Quest For Tires," a separate tamper check freezes the game at the title screen.
In "Sammy Lightfoot," if you disable the tamper check for the self-decrypting protection check, the game starts but level 1 is unwinnable.
Marauder's second tamper check checksums every even byte, to defeat a well known two-byte patch that fooled the first tamper check.
