Long before DRM, companies sought techniques to prevent their software from being copied. One of the most interesting from the 1980s was game manufacturers' inclusion of a code sheet with their games. It was created from a special color of paper and text to prevent copying. Every time the game was started, it would ask for the code that matched a specified number, which you had to copy from the code sheet. If you ever lost or accidentally destroyed the code sheet, you were forced to buy another copy of the game. There were many other methods of copy protection used over the years. Some of them included the following:
Serial and parallel port license connectors
Special CDs or floppy drives that cannot be copied
A license ...