Printers – Output devices GCE AL Computer science topic
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Printers as Output Devices in Computer Systems GCE A level Topic.
II. OUTPUT DEVICES
Printers – Output devices Computer science topic GCE A level.
An output device is an electromechanical device, which converts machine-readable information into human-readable form. The basic functioning of output device is just the opposite of the input device, that is, the data are ‘fed into’ the computer system through the input device, while the output is ‘taken out’ from the computer through the output device. kamerpower.com
II.1 Types of Output
Output is the data that has been processed into useful information. It can be displayed or viewed on a monitor, printed on a printer or listened through speakers or a headset. Generally, there are two basic categories of output: Hard copy output and soft copy output
- Hard Copy refers to the recorded information copied from a computer onto the paper or some other durable surface such as microfilm. Hard copy output is permanent and a relatively stable form of output.
- Soft Copy is the electronic version of an output, which usually resides in the computer memory and/or on the disk. Unlike hard copy, soft copy is not a permanent form of output and is not tangible, that is, it cannot be touched.
II.2 Printers
A printer prints information and data from the computer onto a paper. The quality of a printer is determined by its resolution. Resolution is used to describe the sharpness and clarity of an image. The higher the resolution, the better the image. For printers, the resolution is measured in dots per inch (dpi). The more dots per inch, the better will be the quality of image.
Printers are divided into two basic categories: impact printers and non-impact printers. Impact printers use some sort of physical contact with the paper to make a mark onto it, while non-impact printers use techniques other than to transfer ink onto it.
II.2.1 Impact Printers
An impact printer uses pins or hammers that press an inked ribbon against the paper to make a mark on the paper. Each hammer is embossed with a specific shape, which is transferred onto the paper through the inked ribbon thereby producing a printed character. Some impact printers can print only one character at a time, while others can print an entire line. The three most commonly used impact printers are dot matrix printers, daisy wheel printers and drum printers.
Some characteristics of impact printers are as follows:
- In impact printers, there is physical contact with the paper to produce an image.
- They are relatively cheap. The primary recurring costs for these printers are the ink ribbons and paper.
- Due to being robust and low cost, they are useful for bulk printing.
- They can withstand dusty environment, vibrations and extreme temperature.
- They are ideal for printing multiple copies (i.e. carbon copies) because they can easily print through many layers of paper.
- Due to its striking activity, the impact printers are very noisy.
- Since they are mechanical in nature, they tend to be slow.
a) Dot Matrix Printers
Dot matrix printer (also known as the wire matrix printer) uses the oldest printing technology and it prints one character at a time. It prints characters and images as pattern of dots. The speed of dot matrix printers is measured in characters per second (cps).
b) Daisy Wheel Printer
The major drawback of dot matrix printer is that the patterns of dots that make up each character are visible on the print produced by it, making it look unprofessional. So, to produce professional letter quality documents, a daisy wheel printer is useful. Daisy wheel printers produce high-resolution output and are more reliable than dot matrix printers. They can have speed up to 90 cps. However, daisy wheel printers give only alphanumeric output. They cannot print graphics and cannot change fonts unless the print wheel is physically replaced. Daisy wheel printers are slower and more expensive than dot matrix printers.
c) Drum Printers
The dot matrix and daisy wheel printers are character or serial printers, that is, they print one character at a time. However, drum printer is a line printer; it can print a line in a single operation. Although such printers are much faster than character printers, they tend to be quite loud, have limited multifont capability and often produce lower print quality than most recent printing technologies. Line printers are designed for heavy printing applications.
II.2.2 Non-impact Printers
In this printer, the print head does not make any contact with the paper, and no inked ribbon is required. Ink can be sprayed against the paper and then heat and pressure are used to fuse a fine black powder into the shape of a character. The major technologies competing in the market of non-impact printers are ink-jet and laser.
Some characteristics of non-impact printers are as follows:
- They are faster than impact printers because they have fewer moving parts.
- They are quieter than impact printers
- They possess the ability to change typefaces automatically.
- They produce high-quality graphics.
- They cannot print carbon copies.
a) Ink-jet Printers
An inkjet printer is a printer that places extremely small droplets of ink onto paper to create an image. Ink-jet printers are costlier than dot matrix printers, but the quality is much better. These printers can print any shape of character, which a user can specify as they produce printed output as pattern of tiny dots. Ink-jet printers typically print with a resolution of 600 dpi or more. Due to the high resolution, these printers produce high quality graphics and text printouts. They are also affordable, which appeals to small businesses and home offices.
b) Laser Printers
A laser printer provides the highest quality text and images for personal computers today. It is a very fast printer, which operates on the same principle as that of a photocopy machine. They are also known as page printers because they process and store the entire page before they actually print it. Today, the resolution of most printers is 600 dpi. They are quiet and fast, able to print 4–32 text-only pages per minute for individual microcomputers and up to 200 pages/min for mainframes (more than 2000 lines/min). Laser printers are often faster than ink-jet printers but are more expensive to buy and maintain than the other printers.
c) Hydra Printer
Hybrid document reproduction apparatus (HYDRA) printer, popularly known as all-in-one printer, is a device that consolidates the capabilities of multiple devices in one machine. It may include some or all of the devices like printer, scanner, photocopier and fax machine. Following are the features that must be considered while evaluating these printers: Print speed, Maximum resolution, Memory card compatibility, Scanner resolution, Fax speed.
II.3 Plotters
A plotter is a pen-based output device that is attached to a computer for making vector graphics, that is, images created by a series of many straight lines. It is used to draw high-resolution charts, graphs, blueprints, maps, circuit diagrams and other line-based diagrams. It is similar to a printer, but it draws lines using a pen. Plotters are relatively expensive as compared to printers, but can produce more printouts than standard printers. They are mainly used for computer aided design (CAD) and computer aided manufacturing (CAM) applications such as printing out plans for houses or car parts.
II.4 Computer Output Microfilm
Computer output microfilm (COM) is an extremely high-speed, low-cost process, which records computer-generated information directly from the computer tape or cartridge to a miniaturized microfilm media. The microfilm product is in fiche or roll format, which can be duplicated rapidly and inexpensively. This process can produce data in microfilm form at a highly significant speed from that of a paper printer. COM results in material, space and equipment savings along with mailing costs and information retrieval savings. In addition, hard copy prints can be made without loss of detail, when compared with the original document. The main disadvantage, however, is that it is expensive to install COM and microfilms cannot be read without the assistance of a special reader device.