The Canon EF Lens System
    Canon introduced it's new EF mount for the new line of EOS cameras in 1987, with the unveiling of the EOS 650. What followed was a series of automatic exposure, auto focus, computer controlled electronic cameras. Much of the technology was premiered in the Canon A series of cameras, which had used the old FD series of lenses, but did feature a digital viewfinder, and multi-mode exposure system. One new feature, which had not been on a previous series of Canon cameras, was auto focus. Though the Canon AL-1 had included a focus indicator, in the form of a circle and a pair of arrows, indicating when proper focus was acheived, it had not been linked to the focusing mechanism of the lens.
    Unlike the old FD, FL, and R series of lenses, the new EF type was designed with no mechanical linkages to the camera. Instead each lens has a small digital chip, and motor, and a series of pins connecting to a data bus on the camera's lens mount. The lenses feature a bayonet mount which requies a quarter turn to lock or unlock.

this is not the first time Canon changed it's lens mount.
R, FL, and FD, plus new FD

The two lines coexsisted for a time, but in 1992 canon production of FD lenses ceased.