External components of a computer include the monitor, keyboard, mouse and a wide range of optional peripherals, such as printers and scanners. Any component that does not require opening the computer's case to physically access it can effectively be considered an external component.
The monitor or screen, keyboard and mouse (or trackpad on laptops) are external components that are nearly universal to computers. Other common external components are power supplies, removable storage devices (such as external hard drives), trackballs, drawing tablets, printers, scanners, routers, CD and DVD drives, digital cameras and video recorders, gamepads, joysticks, fax modems, and steering devices for games and simulations, such as wheels and aircraft controls.
A number of standardized ports facilitate the easy connection of external components to a computer. USB ports are widely used for connecting mice, external hard drives, cameras and many other accessories. Ethernet cables for Internet connections and local area networks generally use an RJ-45 jack. PS/2 ports may be used for keyboards or mice. Serial ports may be used for dial-up modems, monitors, mice and printers. VGA connectors may be used for video output. SCSI is a port standard that is found on workstations and servers but is relatively rare in personal computers and laptops.