Computer to plate was a revolution in the printing industry. Printers finally had a way to directly output digital artwork directly onto a printing plate. This single advancement was solely responsible for a drastic increase in quality and productivity within the printing market during the 90's. CTP systems are driven by a computer running a raster image processor (RIP). This RIP computer is responsible for converting image data, like a PDF, into a bitmap used to drive a laser. The laser inside of the CTP machine literally draws the image directly onto a photo sensitive plate.
Plate systems often incorporate a processing system that's filled with common photographic chemicals. Processors can vary but they will often have an activating agent and a fixing agent used to develop the image and then cure it. Some more modern plate types can simply be rinsed with water and then wiped with a gumming agent. Other thermal plates require no processing at all!
RIP software for plate systems should be kept up to date as a direct match to your prepress applications. Whenever there is a large date discrepancy between RIP software and prepress design software we tend to run problems with the way images are rendered, especially with transparencies. Font rewrapping can be a problem too. Keep your software up to date to ensure you never have a job rejected because of some strange RIP error.