Chapter 4: Output Devices Part 2

Chapter 4: Output Devices 

Part 2

Printers

The second most common form of computer output is printed documents. Although a computer can operate perfectly without a printer, it is certainly helpful to the user to have one. People often prefer to get printouts of the work they have done rather than to look at it on the screen it is considered a form of hard copy. 

Types of printers

There are two types of printers

1. Impact Printers
2. Non Impact Printers

1. Impact Printers

Impact printers produce output by striking a ribbon with a hammer. When the ribbon is hit a mark is made on the paper behind it. If carbon paper is put into the printer then an impact printer can print more than one copy of a document at a time. This feature is often used by companies when they print invoices, bills etc. Because of the hammering action impact printers are noisy when they are printing. 

a. Dot Matrix Printer

Dot matrix printers produce an image by hammering a column of 9 or 24 pins against a ribbon. Characters are produced as the print head (which contains the pins) moves across the page. 

Dot matrix printers are cheap to purchase and have low operating costs. The disadvantages of dot matrix printers are that the output quality is poor, it takes a long time to print a document and the noise can be irritating.

Dot Matrix Printer

b. Daisy Wheel Printer

Daisy wheel printers are hardly ever used any more. A daisy wheel printer hammers character stamps (like those on typewriters) against a ribbon to produce high quality text output. The character patterns are all arranged around the edge of a wheel. 

When a letter is to be printed the wheel rotates so that the correct letter is against the ribbon. A hammer then hits the letter against the ribbon to print it on the paper. Daisy wheel printers are very slow and noisy. It is not possible to print graphics using a daisy wheel printer.

Daisy Wheel Printer

c. Line Printer

Dot matrix and daisy wheel printers both print only one character at a time. For that reason they are called Character Printers. In contrast a line printer prints a whole line (typically 80 or 132 characters) of text at a time. These printers are very fast. They are expensive to buy and are used when high volumes of output are required. Example applications include printing telephone bills or bank statements. 

Line Printer

2. Non Impact Printer

Non-impact printers do not produce images by hammering pins or characters against the paper.

a. Ink Jet Printer

Ink jet printers are the most popular type of printer for use at home or in a small business. This is because they are relatively cheap to purchase and can print in color.Typically ink jet printers can produce 360 or 720 dots per inch (dpi). They are slower than laser printers (3ppm) and cost slightly more to run.

Ink Jet Printer

b. Laser Jet Printer

Laser printers are called Page Printers because they print a whole page at a time. A laser beam is used to draw the image to be printed onto a light sensitive Drum. After the image has been drawn on the drum a fine powder ink called Toner is put onto it. The toner only sticks where the laser has drawn the image. The paper then passes over the drum and the toner is transferred onto the paper. 

Laser printers produce very high quality output, are very quiet and very fast. Typical home laser printers can print 8 pages per minute (ppm). Some industrial versions print over 40ppm and can print on both sides of a piece of paper at the same time.

Laser Jet Printer

c. Thermal Printer

Thermal printers are no longer used as printers for PCs. They are however still used in some computer control systems, tills and in many fax machines. These printers print on special heat sensitive paper which is expensive. The image is produced from small dots which are made on the paper by heating it up. The quality is reasonable and graphics can be printed.

d. Photo Printer

A printer specialized for smaller prints such as 4x6" and 5x7".

Photo Printer

e. Mobile Printer

It is said to be "mobile" because it receive wireless signals to print. However, with ink-less printing technology, printers can be mobile in a more essential way. You can carry it around in a pocket or a purse, just like a cell phone.

Mobile Printer

3. Projectors

A Projector is an electro-optical machine which converts image data from a computer or video source to a bright image which is then imaged on a distant wall or screen using a lens system. The cost of a device is not only determined by its resolution, but also by its brightness. The projector serves the following purposes: 

>Visualization of data stored in a computer for presentations.
>Demonstration of program products for a large number of prospective customers.
>The projector replaces the white board as well as written documents. 

Projector

4. Headphone

Speakers and headset is used to get audio output. A system's speaker is the component that takes the electronic signal stored on things like CDs, tapes and DVDs and turns it back into actual sound that we can hear.

Headphone

5. Plotters

A plotter is like a printer that produces hard-copy output. Plotters, which produce high-quality color graphics. Plotters are usually categorized by whether they use pens to create images. A continuous-curve plotter is used to draw maps from stored data.

Plotter