A display device is an output device that usually conveys text, graphics, and video information. Information shown on a display device often is called soft copy, because the information exists electronically and is displayed for a temporal period of time.
Display devices include CRT monitors, flat-panel displays, and high-definition televisions.
- CRT Monitors: Cathode-Ray Tube, an electron tube, or evacuated glass container, having at one end a cathode, or negative electrode, and a device called an electron gun that projects a beam of electrons against a luminescent screen at the opposite end of the tube. A bright spot of light appears wherever the electrons strike the screen. Cathode-ray tubes, or CRTs, are used as picture tubes in television receivers and as visual display screens in radar-receiving equipment, computer installations, and oscilloscopes.
Electrons are emitted from a heated cathode in the electron gun. A series of grids having a positive potential with respect to the cathode accelerate the electrons as they pass. The electrons next pass through a series of doughnut-shaped anodes that focus the stream of electrons so that they strike the luminescent screen as a fine point. Between the electron gun and the screen are either two sets of electric deflecting plates or two sets of magnetic deflecting coils. Electric deflecting plates are used in small CRTs, whereas magnetic deflecting coils are used in large CRTs in which a large deflection is required, as in television tubes.
In CRTs containing electric deflecting plates, a horizontal pair of plates controls the up-and-down motion of the electron beam, and a vertical pair controls the left-to-right motion of the beam. In each pair of plates, one plate has a negative charge of electricity, and the other plate has a positive charge. If the charges are equal in value, the beam will strike the center of the luminescent screen. If the charges are unequal, the electron beam will be deflected. The amount of deflection depends on the voltage applied to the plates. As the signal applied to the horizontal plates varies, so will the spot of light on the face of the tube, which will move up or down in response to the changes in voltage. If the voltage of the vertical plates is varied, the beam of electrons can be made to sweep horizontally across the face of the tube.
Magnetic deflecting coils work in an analogous manner, except that the electron beam is deflected by variations in the strength of the magnetic fields through which it must pass.
A flat-panel display is a light-weight, thin screen that consumes less power than a CRT monitor. Two common types of flat-panel displays are LCD and gas plasma.
- LCD Displays: Are commonly used in laptop computers, handheld computers, digital watches, and calculators because they are thinner and more lightweight than CRT monitors. While most LCD displays are color, even those on newer models of handheld computers, some devices use monochrome LCD displays to save battery power.
Unlike a CRT monitor, an LCD display does not use a cathode ray tube (CR1’) to create images on the screen: it instead uses a liquid crystal display (LCD). A liquid crystal display (LCD) has special molecules (called liquid crystals) deposited between two sheets of material. When an electric current passes through them, the molecules twist, causing some light waves to be blocked and allowing others to pass through, this then creates the desired images on the screen.
- Gas Plasma Monitors: For even larger displays, some large business or power user prefer gas plasma monitors, which can measure more than 42 inches and hang directly on a wall. Gas plasma monitors use gas plasma technology, which substitutes a layer of gas for the liquid crystal material in an LCD monitor. When voltage is applied, the gas glows and produces the pixels that form an image. Gas plasma monitors offer larger screen sizes and higher display quality than LCD monitors but are much more expensive.
History of Printers
In 1953, the first high-speed printer was developed by Remington-Rand for use on the Univac computer.
In 1938, Chester Carlson invented a dry printing process called electro photography commonly called a Xerox, the foundation technology for laser printers to come.
The original laser printer called EARS was developed at the Xerox Palo Alto Research Center beginning in 1969 and completed in November, 1971. Xerox Engineer, Gary Starkweather adapted Xerox copier technology adding a laser beam to it to come up with the laser printer. According to Xerox, “The Xerox 9700 Electronic Printing System, the first xerographic laser printer product, was released in 1977. The 9700, a direct descendent from the original PARC “EARS” printer which pioneered in laser scanning optics, character generation electronics, and page-formatting software, was the first product on the market to be enabled by PARC research.”
According to IBM, “the very first IBM 3800 was installed in the central accounting office at F. W. Woolworth’s North American data center in Milwaukee, Wisconsin in 1976.” The IBM 3800 Printing System was the industry’s first high-speed, laser printer. A laser printer that operated at speeds of more than 100 impressions-per-minute. It was the first printer to combine laser technology and electro photography according to IBM.
In 1992, Hewlett-Packard released the popular LaserJet 4, the first 600 by 600 dots per inch resolution laser printer.
In 1976, the inkjet printer was invented, but it took until 1988 for the inkjet to become a home consumer item with Hewlett-Parkard’s release of the DeskJet inkjet printer, priced at a whopping N 1000.
A printer is a computer peripheral device that puts text or a computer-generated image on paper or on another medium, such as a transparency. Printers can be categorized in any of several ways. The most common distinction is impact vs. nonimpactprinters.
Impact printersinclude Dot matrix and Line printer. These printers print output by stroking with pins of hammers. Normally page travels through the printer and pins or hammers storks against the paper with ribbon and the required output is printed on the paper.
Non-impact printersinclude ink-jet printer, thermal printer and laser jet printer. The output is printed on paper by using special ink. In ink-jet printers, the liquid ink is used. The paper is traveled in the paper and a head sprays the ink on it. In thermal printer no ink is used, instead of a special paper is used. A fax machine is the example of this. A laser jet printer used dry power ink placed in a cartridge. The cartridge also has a drum which is charged magnetically. A charged drum uses the in from cartridge and places it on the paper. Paper then goes through a heater which dries the ink. Other possible methods of categorizing printers include (but are not limited to) the following:
- Print technology:Chief among these, with microcomputers, are pin dot-matrix, ink-jet, laser, thermal, and (although somewhat outdated) daisy-wheel or thimble printers. Pin dot-matrix printers can be further classified by the number of pins in the print head: 9, 18, 24, and so on.
- Character formation:Fully formed characters made of continuous lines (for example, those produced by a daisy-wheel printer) vs. dot-matrix characters composed of patterns of dots (such as those produced by standard dot-matrix, ink-jet, and thermal printers). Laser printers, while technically dot-matrix, are generally considered to produce fully formed characters because their output is very clear and the dots are extremely small and closely spaced.
- Method of transmission:Parallel (byte-by-byte transmission) vs. serial (bit-by-bit transmission). These categories refer to the means by which output is sent to the printer rather than to any mechanical distinctions. Many printers are available in either serial or parallel versions, and still other printers offer both choices, yielding greater flexibility in installation options.
- Method of printing:Character by character, line by line, or page by page. Character printers include standard dot-matrix, ink-jet, thermal, and daisy-wheel printers. Line printers include the band, chain, and drum printers that are commonly associated with large computer installations or networks. Page printers include the electrophotographic printers, such as laser printers.
- Print capability:Text-only vs. text-and-graphics. Text-only printers, including most daisy-wheel and thimble printers and some dot-matrix and laser printers, can reproduce only characters for which they have matching patterns, such as embossed type, or internal character maps. Text-and-graphics printers—dot-matrix, ink-jet, laser, and others—can reproduce all manner of images by “drawing” each as a pattern of dots.
An Example of Printer
- Dot-Matrix Printer:In computer science, any printer that produces characters made up of dots using a wire-pin print head. The quality of output from a dot-matrix printer depends largely on the number of dots in the matrix, which might be low enough to show individual dots or might be high enough to approach the look of fully formed characters. Dot-matrix printers are often categorized by the number of pins in the print head. An example image of a Panasonic KXP2130 Dot Matrix Printer is shown below:
A Dot-Matrix Printers
- Laser Printer, an electrophotographic printer that is based on the technology used by photocopiers. A focused laser beam and a rotating mirror are used to draw an image of the desired page on a photosensitive drum. This image is converted on the drum into an electrostatic charge, which attracts and holds toner. A piece of electrostatically charged paper is rolled against the drum, which pulls the toner away from the drum and onto the paper. Heat is then applied to fuse the toner to the paper. Finally, the electrical charge is removed from the drum and the excess toner is collected. By omitting this final step and repeating only the toner-application and paper-handling steps, the printer can make multiple copies.
The only serious drawback of a laser printer is that it offers less paper-handling flexibility than do dot-matrix printers. Both multipart forms and wide-carriage printing, for example, are better handled by dot-matrix or daisy-wheel printers.
Note: It is a non-impact printer. Sample images are shown below
3. Line Printer:In computer science, any printer that prints one line at a time, as opposed to one character at a time (as with a standard dot-matrix printer) or one page at a time (as with a laser printer). Line printers typically produce the 11-by-17-inch “computer” printouts familiar to many. They are high-speed devices and are often used with mainframes, minicomputers, or networked machines rather than with single-user systems. Types of line printers include chain printers and band printers. The abbreviation LPT originally stood for “line printer”; on MS-DOS microcomputers, the same abbreviation is used for the computer’s parallel output port(s). Sample images of line printers are shown below:
A line Printer
- Thermal Printers: A printer that uses heat to transfer an impression onto paper. There are two kinds of thermal printers:
- Thermal wax transfer: This is a printer that adheres a wax-based ink onto paper. A thermal print headmelts wax-based ink from the transfer ribbon onto the paper. When cool, the wax is permanent. This type of thermal printer uses an equivalent panel of ink for each page to be printed, no matter if a full page or only one line of print is transferred. Monochrome printers have a black page for each page to be printed, while color printers have either three (CMY) or four (CMYK) colored panels for each page. Unlikethermal dye transfer printers, also called dye sublimation printers, these printers print images as dots, which means that images must be ditheredfirst. As a result, images are not quite photo-realistic, although they are very good. The big advantages of these printers over thermal dye transfer printers are that they don’t require special paper and they are faster.
- Direct thermal: a printer that prints the image by burning dots onto coated paper when the paper passes over a line of heating elements. Early fax machines used direct thermal printing.
Sample images of Thermal printers are shown below:
- Portable Printer: This is a small, lightweight printer that allows a mobile user to print from a laptop or handheld computer while traveling. Barely wider than the paper on which they print, portable printers can easily fit in a briefcase alongside a laptop computer. The sample image is shown below:
A Portable Printer
Audio is music, speech, or any other sound. Audio output devices are the components of a computer that produce music, speech or other sounds, such as beeps. Two commonly used audio output devices are speakers and headsets.
Other Output devices
- Data Projectors:
A data projector takes the image that displays on a computer screen and projects it onto a screen so that an audience of people can see the image clearly. Data projectors can be large devices attached to a ceiling or wall in an auditorium, or they can be small portable devices.
- Facsimile (Fax) Machine:
Facsimile (Fax) Transmission, communication system that copies, sends, and receives documents by way of telephone lines. Also called faxing, this method of communication allows people to share exact copies of important papers by duplicating and sending them on one end, and then receiving and reproducing them on the other.
Facsimile machines came into use in the early 20th century when newspaper companies began using them to transmit photographs between branch offices. By the mid-1980s use of desktop facsimile machines had become commonplace for business and personal correspondence throughout the world. More recently, people have used personal computers to send and receive facsimile transmissions, or faxes, eliminating the need for a separate facsimile machine.
The standard facsimile machine works like a combination telephone and photocopier. The user places the documents into a document feeder on the sending machine, and then dials the telephone number of the receiving fax machine. A gear mechanism pulls the original document over an optical scanner. The scanner records variation between light and dark areas of the document as dots arranged in a series of rows or columns. A photoelectric cell converts the dots into electronic impulses, which are then transmitted to the receiving fax machine via telephone lines.
The receiving fax machine decodes the electrical impulses into a series of dots. It sends the decoded signal to a print mechanism built into the fax machine, which prints a duplicate of the original document. International standards ensure that fax machines around the world are compatible with each other.
Older fax machines use special thermal (heat-sensitive) paper, which passes over wires that are heated in response to the electrical impulses transmitted by the sending fax machine. The thermal paper darkens when exposed to the heat of the wire to create a copy. Newer fax machines use small laser printers or ink-jet printers built into the fax machine to reproduce documents. A sample Fax machine image is shown below:
A fax machine
- Multifunction Devices:
A multifunction device (MFD) is a single piece of equipment that looks like a copy machine but provides the functionality of a printer, scanner, copy machine and perhaps a fax machine. Sometimes called a multifunctional peripheral, the features of multifunctional devices vary widely. For example, some use color ink-jet printer technology, while others include a black-and-white laser printer.
This is a device consisting of a video adapter, a monitor, and a keyboard. The adapter and monitor and sometimes, although less commonly, the keyboard are usually combined in one unit. A terminal does little or no computer processing on its own; instead, it is connected to a computer with a communications link over a cable. Keyboard input is sent from the terminal to the computer; video output is sent from the computer to the terminal. Terminals are used primarily in multi-user systems and today are not often found on single-user personal computers. Terminals fall into three basic categories: Dumb Terminal; Intelligent Terminal; Smart Terminal; Terminal Emulation.
Dumb Terminal: It is a terminal that does not contain an internal microprocessor. Dumb terminals are typically capable of displaying only characters and numbers and responding to simple control codes.
Intelligent Terminal: It is a terminal with its own memory, processor, and firmware that can perform certain functions independent of its host processor. A personal computer can be an intelligent terminal with the use of terminal emulation or communications software. Most intelligent terminals, however, have only the capability to reroute incoming data to a printer or video screen.
Smart Terminal: They are input and output device, normally with monitor and keyboard, which has some information processing capability enabling it to run computer programs. A network of computers may include three types of terminals: dumb terminals, which have no ability to process information; smart terminals, which have some processing ability; and intelligentterminals, which are able to process information independently of the network.
Terminals are generally connected to a central computer by wiring or by telephone lines. Early terminals consisted of printers for communicating data output from a remote, central computer, to many users at once. With the incorporation of cathode-ray tube (CRT) technology into terminal displays, terminals eventually became known as video display units (VDUs). Early video terminals displayed characters in a single, preset type style laid out in a rectangular grid.
Dumb terminals did not have a central processing unit (CPU) and therefore had no processing capability. They were totally reliant upon a central computer, usually a mainframe, to run programs and supply data. As dumb terminals gained control devices, eventually including keyboards, they could make specific data requests, and soon input data. Although they are not as fast as smart terminals for some tasks and do not have as many display options, dumb terminals are adequate for many applications.
Like dumb terminals, smart terminals connect to a remote, central computer and rely upon its CPU for the majority of processing power. However, smart terminals have an integrated circuit chip, a microprocessor, for running some programs. This permits the terminal to manipulate data from the central sources, gives the terminal more flexible function overall, and enhances the type of data flowing from desktop to central computer. As microprocessors have grown more powerful, smart terminals have in many instances given way to intelligent terminals.
With processing power growing faster and cheaper and networking becoming easier, computer networks have moved more of the processing function from centralized computers to the desktop CPU-containing computer. Intelligent terminals have a central processing unit (CPU); main random access memory (RAM); keyboard; monitor; mass storage devices such as hard drives, floppy drives and CD-ROM drives; and printers. They can therefore stand alone as computing devices. Most of these terminals are the familiar personal microcomputers known to most computer users.
Networks based on smart or intelligent terminals, especially local area networks (LANs), are known as distributed networks because they spread their overall processing capabilities between multiple locations. Virtually any computer can now become, in effect, a smart or intelligent terminal to a massive worldwide computer network by simply connecting to the Internet.
For simple data entry and recall such as making and confirming airline reservations and similar tasks in the banking, retail, insurance, and travel industries, dumb terminals remain in wide use. Recently, the computer industry has indicated interest in developing stripped-down PCs called network computers (NCs). These would be inexpensive relative to current PCs and would be designed primarily to access the Internet. Since they would derive most of their processing power from larger computers on the Internet, they would be either smart or dumb, depending on their specific application. The idea of using these stripped-down PCs as terminals for the Internet has renewed interest in the concept of smart and dumb terminals.
These are the last parts of the hardware components. They are aid other hardware e.g. protection
A. system fan: to regulate temperature the system unit
B. computer case/cover to protect the system unit from humidity and dust.