What is "DX encoding" of roll film, such as 135 format film used in 35mm cameras? How does it work? When was it introduced? Is there anything else I need to know about using DX encoded film in a camera that can read the encoding? How about in a camera that can not read the encoding? For that matter, how can I tell if my film camera can read DX encoded film?
DX coding has been used since the early- to mid-1980s. You can tell if your camera has DX code capability most easily by looking at the chamber where the film cartridge goes. There will be several sets of metal contacts along the right side of the chamber (assuming traditional loading where the cartridge is to your left, and feeds to the right). These check for conductivity in the same place on the cartridge - the chrome squares on the code. The black squares are non-conductive.
Non-DX-coded film will work in DX-code-using cameras as long as they have a provision to manually set ISO/ASA (most SLRs do; many point-and-shoots don't). DX-coded film will work in any camera that does not support DX coding; just set the ISO manually as normal.
That DX is a barcode system stating ISO, printed on the film canister, so the camera and photo finisher can identify it. The canister has a conductive/nonconductive code that electrical sensors in camera can read.
Wikipedia says it started in 1983 and has details. See your camera manual, but if the camera offers it, DX is probably an item in the dial list for ISO speed, which selecting DX should set the ISO speed automatically.