Difference in EF & EF-S Lens Attachment

When mounting a lens to my 40D the EF lens aligns with a red dot at 12 o'clock on the camera body but the EF-S aligns with a white dot a few degrees clockwise from 12 o'clock. Why? Do the 5D and 1D bodies not have the white dot?

I tried a search but didn't get any answers and I even checked the manual but it just acknowledged the dots were there for the different lenses.

no white dots on the 5D and 1D bodies.

EF-S lenses are designed to only mount on EF-S compatible bodies (or conversely, non-EF-S bodies won't mount EF-S lenses). 5D and 1D series are not EF-S compatible.

That is pretty much what I thought. I have compared my EF 28-135 to my EF-S 10-22 and it appears that the EF-S lens would probably mount on a 5D/1D body but that the contacts would not line up properly. Is that the case or is there enough difference in the key ways on the camera mounts that the EF-S will not mount on the 5D/1D without modification. I do understand the EF-S was not designed for the 5D/1D but I was just curious about the mechanics of the mounts.

Sparky98 wrote in post #4873648
That is pretty much what I thought. I have compared my EF 28-135 to my EF-S 10-22 and it appears that the EF-S lens would probably mount on a 5D/1D body but that the contacts would not line up properly. Is that the case or is there enough difference in the key ways on the camera mounts that the EF-S will not mount on the 5D/1D without modification. I do understand the EF-S was not designed for the 5D/1D but I was just curious about the mechanics of the mounts.

The part of an EF-S lens that makes the EF-S lenses impossible to mount on cameras not designed for them is the round plastic projection that is just inside the metal mount ring and projects about 1/4" further into the camera than the metal mount ring. The round projection won't fit through the rectangular hole (a "mask") which is just behind the camera's mount in cameras other than those designed to accept the EF-S lenses. The rectangular mask is set deeper in those cameras designed for the EF-S lenses so that the projection on the EF-S lens has somewhere to go.

Thanks for all the information. My curiosity is sated for now.