TOMMY was a little bit different as far as speaker placement, but generally 4 track was 4 channels- Left, Right, Center, (which would have been placed behind the screen and one Surround channel that was fed to all the side and back speakers.
Current theatrical systems can have as many as 8 channels- SDDS has 1 is for the bass channels fed to the subwoofers, the other channels are
Left, Left-center, Center, Right-center, Right, Left Surround, Right Surround, Rear Surround. This is mostly available for huge screens where the movement of the sounds on the five front channels can be heard.
Predominantly, what you hear in the theater is mostly 5.1 (left, center, right, left surround, right surround, subwoofer) or 6.1 which adds the rear surround. Formats which can be matched in a home theater setup, wonderfully enough.
Much more involving than mono, which is 1 channel coming out of all the speakers, with no stereo separation of music, or on-screen effects.