Originally posted by linse
Digital and film cameras work the same way when you use exposure compensation because it involves the camera's metering.
If you use any camera on manual exposure: Assuming the shutter and aperture are set for the correct exposure to start with, if you then dial in positive exposure compensation, the camera's metering will then indicate that the scene is underexposed. In turn you will have to decrease the shutter speed or open up the aperture to match the new metered exposure.
It is true changing the compensation and ISO on a non-digital alters the metering. However, this does not make you film more sensitive to light unless you push process the whole roll of film. If you haven't being push-processing your film and is using negative exposure compensation/increase ISO settings to increase the shutter speed in low light situations, you have been underexposing your negatives. It may not be obvious to you if the photo labs have compensated for the underexposure. However, if you shoot slides, it will be very obvious. You can underexpose film more and still get away with it as film has a greater lattitude compared to CCD/CMOS chips.