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PRINTER A printer is an external hardware output device that takes the electronic data stored on a computer or other device and generates a hard copy of it. A printer is also an output device that prints characters, symbols, and perhaps graphics on paper. The printed output is generally referred to as hardcopy because it is in relatively permanent form. Softcopy refers to temporary images such as those displayed on a monitor. Printers are categorized according to whether or not the image produced is formed by physical contact of the print mechanism with the paper.

IMPACT PRINTERS An impact printer has mechanisms resembling those of a typewriter. It forms characters or images by striking a mechanism such as a print hammer or wheel against an inked ribbon, leaving an image on paper. Impact printers are dying out; however, you may still come in contact with a dot-matrix printer. A dot-matrix printer contains a print head of small pins that strike an inked ribbon, forming characters or images. Print heads are available with 9, 18, or 24 pins; the 24-pin head offers the best print quality. Dotmatrix printers permit a choice between output of draft quality; a coarser-looking 72 dots per inch vertically, which may be acceptable for drafts of papers and reports, and near-letter-quality, a crisperlooking 144 dots per inch vertically, which is more suitable for a finished product to be shown to other people. Dot-matrix printers print about 40-300 characters per second (cps) and can print some graphics, although the reproduction quality is poor. Color ribbons are available for limited use of color. Dot-matrix printers are noisy, inexpensive, and they can print through multipart forms, creating several copies of a page at the same time, which nonimpact printers cannot do.

Another type of impact printer is not used with microcomputers. Large computer installations use highspeed line printers, which print a whole line of characters at once rather a single character at a time. Some, called chain printers, contain characters on a rotating chain; others, called band printers, contain characters on a rotation band. Speeds of up to 3000 lines a minute may be possible with these machines.

NONIMPACT PRINTERS Nonimpact printers, used almost everywhere now, are faster and quieter than impact printers because they have fewer moving parts. Nonimpact printers 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.

Laser Printer: Like a dot-matrix printer, a laser printer creates images with dots. However, as in 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. – There are good reasons why laser printers are so popular. They produce sharp, crisp images of both text and graphics, providing resolutions from 300 dpi up to 1200 dpi, which is near-typeset quality (NTQ). 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. (Pages with more graphics print more slowly.) They can print in many fonts (type styles and sizes). The more expensive models can print in different colors. – 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 color 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. To be able to manage graphics and complex page design, a laser printer works with a page description language, a type of software that has become a standard for printing graphics on laser printers. A PDL (page description language) is software that describes the shape and position of letters and graphics to the printer. PostScript, from Adobe Systems, is one common type of page description language; HPGL, Hewlett-Packard Graphic Language, is another.

Ink-jet printer: Like laser and dot-matrix printers, ink-jet printers also form images with little dots. Inkjet printers spray small, electrically charged droplets of ink from four nozzles through holes in a matrix at high speed onto paper. – Ink-jet printers can print in color and are quieter and much less expensive than a color laser printer. However, they are slower and print in a somewhat lower resolution (300-720 dpi) than laser printers. Some new, expensive ink-jet printers print up 1200 or 1400 dpi. High resolution output requires the use of special coated paper, which costs more regular paper. And, if you are printing color graphics at a high resolution on an ink-jet printer, it may take 10 minutes or more for a single page finish printing. – A variation on ink-jet technology is the bubble-jet printer, which use miniature heating elements to force specially formulated inks through print heads with 128 tiny nozzles. The multiple nozzles print fine images at high speeds. This technology is commonly used in portable printers.

Types of Printers •

3D printer: is a device that creates a physical object from a digital model by layering materials. 3D printers use materials such as metal alloys, polymers, plastics, or even food ingredients.

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AIO (all-in-one) printer: AIO is short for all-in-one. It is used to describe a hardware device such as an all-in-one printer that is a printer, fax, and scanner all in one device.

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Dot matrix printer: The term dot matrix refers to the process of using dots to form an image. In a dot matrix image, the quality is determined by the number of dots per inch. Dot matrix printers use print heads to shoot ink or strike an ink ribbon to place hundreds to thousands of little dots to form text and images

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Inkjet printer: The most popular printer for home computer users that prints by spraying streams of quick-drying ink on paper. The ink is stored in disposable ink cartridges, and often a separate cartridge is used for each of the major colors. These colors are usually CMYK (cyan, magenta, yellow, and black). The picture is an example of a computer inkjet printer. Although inkjet printers themselves are often relatively inexpensive, the ink cartridges used in the printers can increase the overall cost of the printer.

•

Laser printer The laser printer was first developed at Xerox PARC by Gary

Starkweather and

released

in 1971that utilizes laser technology to print images on the paper. Laser printers are often used

for

corporate,

school,

and

other

environments that require print jobs to be completed quickly and in large quantities. In the picture, is a Lexmark C782n laser printer and a good example of a laser printer. As the image shows, a laser printer is usually larger than an inkjet printer found in most homes. How a laser printer works and its printing steps. Below is a chart of the steps a laser printer takes to print. •

Cleaning: This process removes the prior image information and toner from the drum.

•

Conditioning: The corona wire applies a uniform, positive charge to the photoreceptor drum.

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Writing: The image to be printed is drawn onto the drum by using a laser to "carve out" positive charges and leave behind negative ones. As an aside, the laser in the printer uses light sources like LED or LCS (liquid crystal shutter).

•

Developing: The toner in the ink roller is ionized with a positive charge so that it will be attracted to the areas on the drum previously given a negative charge by the laser.

•

Transfer: The toner of the drum is transferred to the paper by either a positively ionized field (created by a transfer corona wire) or by a transfer roller in newer printers. The toner is not yet permanently set on the paper and requires the last stage.

•

Fusing: Heat and pressure are applied to the paper and toner by two fuser units. The toner melts and is pressed into the paper like doing an iron-on transfer to a T-shirt.

PRINTER PORTS The parallel port is found on the back of the computer and is part of the motherboard.

Cat 5 Connector Alternatively referred to as an Ethernet cable or LAN cable, a Cat 5 or category 5 is a network cable that consists of four twisted pairs of copper wire terminated by an RJ-45 connector. Cat 5 has a maximum length of 100m, exceeding this length without the aid of bridge or other network device could cause network issues

Serial Port An asynchronous port

on

the computer used

to

connect a serial device to the computer and capable of transmitting one bit at a time.

Short for universal serial bus, USB (pronounced yooes-bee) is a plug and play interface that allows a computer to communicate with peripheral and other devices. USB-connected devices cover a broad range; anything from keyboards and mice, to music players and flash drives.

MODEM Modem is abbreviation for Modulator – Demodulator. Modems are used for data transfer from one computer network to another computer network through telephone lines. The computer network works in digital mode, while analog technology is used for carrying massages across phone lines. Modulator converts information from digital

mode

to

analog

mode at

the

transmitting

end

and demodulator converts the same from analog to digital at receiving end. The process of converting analog signals of one computer network into digital signals of another computer network so they can be processed by a receiving computer is referred to as digitizing. When an analog facility is used for data communication between two digital devices called Data Terminal Equipment (DTE), modems are used at each end. DTE can be a terminal or a computer.

The modem at the transmitting end converts the digital signal generated by DTE into an analog signal by modulating a carrier. This modem at the receiving end demodulates the carrier and hand over the demodulated digital signal to the DTE.

The transmission medium between the two modems can be dedicated circuit or a switched telephone circuit. If a switched telephone circuit is used, then the modems are connected to the local telephone exchanges. Whenever data transmission is required connection between the modems is established through telephone exchanges. Ready to Send To begin with the Data Terminal Equipment or DTE (better known as a computer) sends a Ready To Send or RTS signal to the Data Communication Equipment or DCE (better known as a modem). This is sometimes known as a wakeup call and results in the modem sending a Data Carrier Detect or DCD signal to the receiving modem. There then follows a series of signals passed between the two until the communication channel has been established. This process is known as handshaking and helps to explain why, even now, some companies like CompuServe use the symbol of two hands grasping each other to mean being on-line. Of course, after that all it takes is for the second modem to send a Data Set Ready or DSR signal to its computer and wait for the Data Terminal Ready or DTR reply. When that happens the first modem sends a Clear To Send or CTS signal to the computer that started the whole process off and data can then be transmitted. It is as simple as that. Alternatively, for anyone confused by what the entire Internet industry dubs TLA's which means Three Letter Acronyms, the following diagram should help.

It only looks confusing. Take a second look and everything will soon become obvious. By way of completeness, these signals are all sent through different pins in the plug which is why the handbooks for all modems and printers carry a pin diagram somewhere in the section on troubleshooting. They are also standardized after the industry leaders met to agree standards for a whole range of peripheral equipment. The Recommended Standard for cable was number 232 which explains that one technical term probably everybody has heard of: RS 232. Of course, that still leaves the question of exactly how data is transferred from one computer to another; something that is more of a problem than might first appear mainly because the phone lines are analogue while computers are digital. In simple terms this means a telephone signal is constantly changing. To understand that just think of a sine wave as produced on an oscilloscope. The signal might be constant, but it is constantly changing from positive to negative and back again in a series of smooth curves. Computers, on the other hand, can only understand information when it is presented as a string of binary digits so the idea is to map digital output onto an analogue signal. Without going into technical details this is done by superimposing different frequencies onto the analogue signal (which then becomes known as the carrier wave). Different frequencies can then represent different groups of binary digits in a process which is known as modulation when it is being transmitted and

demodulation when it is decoded at the receiving end. Naturally two way communication is achieved by having a single device being capable of both modulation and demodulation, from which the unit takes its name: the modem. From this it becomes obvious that the more frequencies that can be superimposed on the carrier wave the faster data can be transmitted. Alternatively, to take a different point of view, the more data there is to be transmitted so the more frequencies are needed. Unfortunately it is only possible to send a limited number of frequencies at the same time, known as the bandwidth, which means communication takes that much longer as the size of the signals steadily increases. Now that pictures, sound and even video sequences are transmitted over the Internet on a regular basis, and as these all call for massive data files, the amount of available bandwidth is likely to be a problem for some time. Finally, as the whole process comes down to sending binary digits or bits over a phone line the speed of the system is expressed as Bits Per Second or BPS which is a figure quoted by all the modem manufacturers. Unfortunately when it comes to data communications there is a lot more involved than just how fast bits can be sent down a phone line. There is also the problem of what those bits mean and how they can be assembled into something intelligible at the far end. Here a whole range of issues need to be addressed and so it might be a good idea to briefly look at the first of these which are the transmission protocols. Types of Modems • Modems can be of several types and they can be categorized in a number of ways. • Categorization is usually based on the following basic modem features: 1. Directional capacity: half duplex modem and full duplex modem. 2. Connection to the line: 2-wire modem and 4-wire modem. 3. Transmission mode: asynchronous modem and synchronous modem. Half duplex and full duplex Modems Half duplex 1. A half duplex modem permits transmission in one direction at a time. 2. If a carrier is detected on the line by the modem, I gives an indication of the incoming carrier to the DTE through a control signal of its digital interface.

3. As long as they camel' IS being received; the modem does not give permission to the DTE to transmit data.

Full duplex • A full duplex modem allows simultaneous transmission in both directions. • Therefore, there are two carriers on the line, one outgoing and the other incoming. Wire and 4-wire Modems • The line interface of the modem can have a 2-wire or a 4-wire connection to transmission medium. 4wire Modem • In a 4-wire connection, one pair of wires is used for the outgoing carrier and the other pair is used for incoming carrier. • Full duplex and half duplex modes of data transmission are possible on a 4- wire connection. • As the physical transmission path for each direction is separate, the same carrier frequency can be used for both the directions.

2-wire Modem • 2-wire modems use the same pair of wires for outgoing and incoming carriers. • A leased 2-wireconrlection is usually cheaper than a 4-wire connection as only one pair of wires is extended to the subscriber's premises. • The data connection established through telephone exchange is also a 2-wire connection.

• In 2-wire modems, half duplex mode of transmission that uses the same frequency for the incoming and outgoing carriers can be easily implemented. • For full duplex mode of operation, it is necessary to have two transmission channels, one for transmit direction and the other for receive direction. • This is achieved by frequency division multiplexing of two different carrier frequencies. These carriers are placed within the bandwidth of the speech channel.

Asynchronous & Synchronous Modems Asynchronous Modem • Asynchronous modems can handle data bytes with start and stop bits. • There is no separate timing signal or clock between the modem and the DTE.

• The internal timing pulses are synchronized repeatedly to the leading edge of the start pulse .

Synchronous Modem • Synchronous modems can handle a continuous stream of data bits but requires a clock signal. • The data bits are always synchronized to the clock signal. • There are separate clocks for the data bits being transmitted and received. • For synchronous transmission of data bits, the DTE can use its internal clock and supply the same to the modem....