What is a computer?
Characteristics of a monitor
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- Digital / Multimedia Projector
- Headphones/Earphones Headphones
- Line Printers: A high-speed printer capable of printing an entire line at one time
- Dot-matrix printer
- Laser Printer
- 4-32 text-only pages per minute
Characteristics of a monitor: Resolution: The resolution of a monitor refers to the clarity of its images. It shows how densely packed the pixels (tiny dots that creates the image on a monitor) are. The more pixels used (often expressed in dots per inch), the sharper the image. Refresh rate: How many times per second the screen is refreshed (redrawn). To avoid flickering, the refresh rate should be at least 72 Hz. Dot pitch : The amount of space between each pixel, the smaller the dot pitch, (space between pixels) the sharper the image. Digital / Multimedia Projector Digital projectors are used in situations when a very large viewing area is required, for example during presentations, for advertising, or in your home for watching movies. A projector connects to a computer, a DVD player or a satellite receiver just like an ordinary monitor. The image is produced inside the device and then projected out through a large lens, using a powerful light source. Loudspeaker Allows you to hear music or sounds from your computer. They convert electrical signals into sound waves. Loudspeakers are essential for applications such as music editing, video conferencing, watching movies, etc. 
Headphones/Earphones Headphones are a pair of small loudspeakers that are designed to be held in place close to a user's ears. Headphones either have wires for connection to a signal source such as an audio amplifier, radio, CD player, portable media player or mobile phone, or have a wireless receiver, which is used to pick up signal without using a cable. The in-ear versions are also known as earphones or earbuds. Hard Copy Devices 
Printers Printers are output devices used to create permanent output on paper. Printers can be divided into two main categories: Impact and Non Impact. Impact Printers: Uses hammers or pins to strike against a ribbon on paper to print the text. They are of two types. (i) Character Printers: It prints only one character at a time and has a relatively slow speed. Eg. Dot matrix printers. (ii) Line Printers: A high-speed printer capable of printing an entire line at one time. A fast line printer can print as many as 3,000 lines per minute. The disadvantages of line printers are that they cannot print graphics, the print quality is low, and they are very noisy. I  mpact printers
 Dot-matrix printer prints characters as combination of dots. They print about 40-300 characters per second (cps) and can print some graphics, although the reproduction quality is poor. Colour ribbons are available for limited use of colour. Dot-matrix printers are noisy, inexpensive, and they can print through multipart forms, (using carbon paper) creating several copies of a page at the same time, Also used to print on continuous paper.
Daisy-Wheel Printer A  type of printer that produces letter-quality type, the daisy-wheel is a serial printer. It works on the same principle as a typewriter. Daisy-wheel printers cannot print graphics, and in general they are noisy and slow, printing from 10 to about 75 characters per second. As the price of laser and ink-jet printers has declined, and the quality of dot-matrix printers has improved, daisy-wheel printers have become obsolete.
Non Impact Printers Non Impact printers, used almost everywhere now, are faster and quieter than impact printers because they have fewer moving parts. They form characters and images without direct physical contact between the printing mechanism and the paper. Two types of nonimpact printers often used with microcomputers are laser printers and ink-jet printers.
A laser printer creates images with dots. Like a photocopying machine, these images are created on a drum, treated with a magnetically charged ink-like toner (powder), and then transferred from drum to paper. They produce sharp, crisp images of both text and graphics and they are quiet and fast. They can print 4-32 text-only pages per minute for individual microcomputers, and more than 120 pages per minute for mainframes. They can print in many fonts (type styles and sizes). Laser printers have built-in RAM chips to store documents output from the computer. If you are working in desktop publishing and printing complicated documents with colour and many graphics, you will need a printer with a lot of RAM. Laser printers also have their own ROM chips to store fonts and their own small dedicated processor. I  nk-jet printer: It prints characters by spraying patterns of ink on the paper from a nozzle or jet. Ink-jet printers can print in colour and are quieter and much less expensive than a colour laser printer. However, they are slower and print in a somewhat lower resolutions.
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