Full Auto (The green A+ on the mode dial) puts the camera into a mode where it has the simplicity of a point & shoot camera -- but that means it hides many options to simplify the interface and function. Many things that the camera is fully capable of changing are locked-out from change when in that mode to prevent a non-advanced user from making a change that might adversely impact their photos ... and a non-advanced user might not know that even made the change.
Program mode is similar to full auto mode, EXCEPT that while program automatically determines which settings to use for an automatic shot... you can override the default choices that the camera makes. You can increase or decrease exposure using exposure compensation. You can use "Program Shift" to select alternative "equivalent" exposures (for any given amount of light, there are probably at least a half-dozen combinations of shutter speed and aperture opening size that will collect the same amount of light, but trading stops of aperture for stops of shutter speed has a creative impact on the resulting photo.) This gives you creative control over the photo that you would not have in full A+ mode. If you don't choose to override anything in Program mode then it's just like shooting in A+ mode.
Since Program mode (as well as Tv, Av and Manual mode) expands your ability to take control of the camera, the menu options with many more configuration choices will show up when the mode dial is in one of those modes.
Tim Campbell
5D III, 5D IV, 60Da
