CR= Computed radiography. It uses an imaging plate in a cassette instead of film to capture the image. It is then fed into a special processor that extracts the image and erases the plate for the next use. Initial investment is more but no chemicals, no silver and the image is able to be manipulated.
DR= digital radiography. It is similar to CR but instead of a plate in a cassette, it has an imaging detector that is connected directly to a computer to get the image. It is either in the table or what looks like a cassette but wired to the portable x-ray machine.