picture archiving and communication system. Pan and zoom - the ability to select and magnify a region in the display. Peripheral - a device that is connected to a computer and performs a function. Scanners, mouse pointers, printers, keyboards, and monitors are examples of peripherals. Phosphor - the coating on the inside of a CRT or monitor that produces light when it is struck by an electron beam. Pixel (picture element) - the smallest piece of information that can be displayed on a CRT. It is represented by a numerical code within the computer and displayed on the monitor as a dot of a specific color or intensity. An image is composed of a large array of pixels of differing intensities or colors. Protocol - a set of guidelines by which two different computer devices communicate with each other.