Color64 is a computer BBS system that was very popular for the Commodore 64 during the 1980s. It was written by Greg Pfountz. Color64 was advanced for its time. The I/O was all written in machine language. It was also composed in modules, each written in BASIC. Each module would be loaded into memory as a user went from one part of the system to another. For example, the login module was what handled the answering of the phone and the verification of login info. It would then load the main menu module. Going into the message boards would load the message board module. Online games worked the same way.
Because the Commodore 1541 and Commodore 1571 disk drives were slow, most BBSs would use memory expansion module. This would serve as a RAM disk and allow all modules to be loaded quickly.