Instruments for interpretation and communication between human and computers are output devices. These devices take machine coded output results from the processor and convert them for human reading. Display screens and printers are output devices.
Visual Display Units (VDU): It is an output media. These are called Cathode Ray Tubes (CRTs) (an electronic tube with screen for display), Video Display Terminal (VDTs) etc. A characteristic feature of CRT is the cursor (blinking light) which indicates the position of the character on the screen. The display that appear on the screen is know as Display Memory. CRTs display 24 lines and upto 132 characters. Scrolling may be done to see more lines.
Printers: Printers fall into three basic categories. They are Page Printers, Line Printers and Character Printers. Page Printers provide a complete page image in a single operation by laser or electro-static methods. Line Printers produce a line of characters all at once. Most line printers produce 120-144 characters per line. Most common is 132 characters. Character Printers form one letter at a time. There are two ways to do this. Letter Quality create fully formed letters like a typewriter. Dot Matrix create characters as a series of rectangular do matrix. It is faster than letter quality, but print quality is not so good.
Other Printers are Impact Printers where the print head strike the paper. Non-Impact Printers which minimize the amount of physical movements. Thermal Printers form characters by burning them on specially treated paper.
Electro Static Printers: Operate similar to thermal printers using toner etc.
Ink Jet Printers: Squirt stream of ink to the surface of the paper which dries instantly.
Peripherals: The input/output and secondary storage units are sometimes called peripherals because they are located usually near the processor.