Floppy Disk Preservation Project
Copy Protection Methods

Copy Protection Used on PC-Compatible Computers

Background

The PC floppy disk system is based on the off-the-shelf NEC uPD765A (or compatibles, such as the Intel 8272A) floppy disk controller chip. This chip controls all communication between the disk drive and the computer, which limits what the PC is able to write to the floppy disk to the standards provided by this chip. These limitations are what is exploited for copy protection. The disk drives most commonly found on the PC are 5.25" and 3.5" in double-density or high-density. Only the original IBM PC (1981) used a single-sided 5.25 disk drive - all following models had double-sided drives.

IBM INTERLOCK

Electronic Arts used "IBM INTERLOCK"
SuperLok
Apple ][ Registry Stats
Total Registered: 89

Top 5 Earliest Serials
Unknown: A2S1-0001
Jef Raskin: A2S1-0002
Bob Bishop: A2S1-0013
unknown: A2S1-0047
Geoff Harrison: A2S1-0097

Latest Serial
Paul Hagstrom:
A2S2-1497165

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C64 Registry Stats
Total Registered: 2422

Top 5 Earliest Serials
Unknown: 0019
Charles Lynch: 0021
John Justice: s00001281
c64web.com: S00001390
Matteo Caccia: S00001576

Latest Serial
Sos:
HB41651823E

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Disk Database Stats
Titles archived: 3532
Titles verified: 1348

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All content copyright (c) 1971- by Peter Rittwage. All programs mentioned are copyrighted by their respective owners.