Computer System
Intoduction
A computer system, for being useful has to communicate with its environment through some means known as Computer Peripherals or Input/Output Devices. Computer peripherals may be divided into three broad categories namely Input Devices, Output Devices and Input/Output Devices.
Input Devices
Keyboard
The computer keyboard is most commonly used input device to enter number, alphabets and special characters into the computer. The keyboard are also used to type in the commands to direct the computer to perform certain tasks. A keyboard has alphabetic and numeric key for entering the text numeric data. There are a certain number of iditing keys and a number of funtion key which are used to invode function directly. The Caps Lock/Num Lock/Scroll Lock key is called Toggle keys and used to turn on/off the feature. The Ctrl/alt Keys are called keyboard come with separate numeric Pad/section to enter numerical values.
Pointing Devices
The graphical user interfaces (GUIs) which are extensively used require some kind of devices for positioning the on-screen cursor. Some common pointing devices are mouse, trackball, touch pad, track point, graphics tablet, and joystick and touch screen. Pointing devices are connected to a PC via a USb port.Mouse
The mouse is most popular pointing device used by users with one hand. In older mouse, a ball in the buttom of the mouse rolls on the surface as we move the mouse and internal rollers sense the movement of ball and transmit the information to the computer through the mouse cord. The modern optical mouse does not use a rolling ball, but instead use a light and small sensor to detect the motion of the mouse by tracking a small image of the desk surface. Acordless or wireless mouse interconnects with the computer via radio waves.
Touch Pad
Most of the laptops are equipped with a touch pad pointing device. User moves the on screen cursor by sliding his/her finger along the surface of the touch pad. The left/right Click buttons are located below the pad. Touch pads have advantage over mouse that they take much less room to use. Also they don't have any moving parts.Track Point
Some sub-notebook computers such as IBM Thinkpad which lack room even for a touch pad, incorporates a TrackPoint, a small rubber projection embedded amid the keys of the keyboard. The TrackPoint acts like a small joystick that can be used to control the position of the cursor.Trackball
The trackball is like an upside is like an upside-down mouse, with ball locate on the top. We use fingers to roll the trackball and internal rollers sense the motion which is transmitted to the compute. Trackball has the advantage over Mouse is that the body of the trackball remains stationary on the desk; we don't need much room to use the trackball. Nowadays optical trackballs are available which don't have rollers and there is no problem of dirt in its wheels.
Joysticks
Joysticks and other common game controllers can also be associated to a computers as pointing device. They are generally used for playing games.
Graphics Tablet
A graphics tablet contains an electronic writing area and a special pen which works using it. Graphics tablets allow the artists to create graphical images with motions and actions similar to using more traditional drawing devices. The pen of the graphics tablet is pressure sensitive, so pressing harder or softer can result in brush strokes of different width.
Scanners
A scanner is a device that enters the printed page or graphic in computer by digitizing it, producing an image made of tiny pixels of diverse brightness and color values which is sent to the Computer. It uses laser technique to convert the printed information being scanned can be anything like handwritten text, images, diagrams etc. Once scanned it can be stored in Computer or printed through a Printer.
Midi Devices
MIDI (Musical Instrument Digital Interface) is a system intended to transmit information between electronic musical instruments. A MIDI musical keyboard can be connected to a computer and permit a performer to play music that is captured by the computer system as a sequence of notes with the associated timing.Magnetic Ink Character Recognition (MICR)
Magnetic Ink Character Recognition Code (MICR Code) is a character-recognition technology used mainly by the banking industry to ease the processing and clearance of cheques and other documents. It converts them into digital data for understanding of computer.Optical Mark Reader (OMR)
There are specail scanners to scan and identify a pre-specified type of marks (human-marked data) made by Pencil or Pens. Most common example is answer sheets used in the examination. OMR is used to scan the answer sheets and produce result as output. OMR is also used in surveys, polls and tests.Optical Character Recognition (OCR)
Optical character recognition (optical character reader) (OCR) is the electronic conversion of images of typed, handwritten or printed text into machine-encoded text. It is widely used as a form of data entry from printed paper data records, whether passport documents, invoices, bank statments, computerized receipts, business cards, mail, prinouts of static-data, or any suitable documentation. It is most common method of digitizing printed texts so that it can be electonically idited, searched, stored more compactly, displayed on-line, and used in machine processes such as machine translation, text-to-speech, key data and text mining.Bar Code Reader
Bar Code is a machine readable data representation of an object and is used to identify an object uniquely. Originally barcodes represented data by varying the widths and spacings of paralled lines but later they evolved into rectangles, dots, hexagons and other geometric patterns in two dimensions (2D). These are specifically used in shopping malls and departmental stores for quick billing and inventory management. A Special handheld device (Bar Cde Reader) connected to a computer/terminal is used to read the code and identify the item.Speech Recognition Device (Microphone)
Microphone is an input device used to input audio data into a computer. It is connected to a computer system through a single wire and users may use a mouthpiece shape like device to capture the audio.Webcam (Web Camera)
This is a digital camera connected to the computer and can feed images/videos to computer networks through the computer. The camera is focused on the input item to take a picture and convert it to a machine readable format for storing in a computer system.Output Device
Monitor
To produce a soft copy of output, the most popular device is a Monitor. It allows users to view/read the output on a Computer Screen.CRT Monitor
The classical output device of a personal computer has been the CRT monitor. It is just like a TV set. A CRT monitor encompasses a big cathode ray tube that uses an electron beam of varying power to "paint" a picture onto the color phosphorescent dots on the inside of the screen. Monitor screen size is measured diagonally across the screen, in inches. The resolution of the monitor is maximum number of pixels it can display horizontally and vertically such as 800*600, 1024*768 etc. Pixels are the small dots that make the image displayed on the screen. The spacing of the screens tiny phosphor dots is called the dot pitch. A screen with smallwer dot pitch produces sharper images.
Flat Panel Monitor
A flat panel monitor usually uses an LCD (Liquid Crystal Display) screen to show output from the computer. The LCD is made of several thin layers that polarize the light transmitting through them. The polarization of one layer, containing long thin molecules called crystal displays can be controlled electronically at each pixel, blocking varying amounts of the light to create a pixel lighter or darker. LED (Light Emitting Diode) and Plasma Displaysare also flat panel technologies but LCDs are most popularly used in computers especially in laptops.Flat panel displays are much lighter and less bulky than CRT monitors. The lartest LCD screens use transparent thin film transistor (TFT) controlling each pixel, so the picture quality and viewing angel are much improves. LED monitors use light emitting diodes that acts as a performance booster in the monitors. Basically LED monitors are the LCD monitors with a LED backlight to power up the LCD panel.
Printer
Printer provide information in a permanent readable format also known as Hard Copy. Usually output is printed on a paer. The printer output quality is measured in terms of DPI (Dots per Inches). The printers can be classified broadly into Impact and Non-Impact Printers.Impact Printers
character Printer
These types of printers usually print one character at a time. Most popular examplesare dot Matrix and Daissy Wheel Printers. Dot matrix printers are small electromagnetically activated pins in the print head, and an linked ribbon to produce images by impact. There are used in big businesses where continous printing is to be done on 80 columns and 132 columns stationary.
Line Printer
a line printer prints a complete line at a time. Traditionally line printers were characterized as Chain Printers and Drum Printers. These types of printers use a print head consisting of pins which are moved by electromechanical mechanism to strike a ribbon placed between printer head and the paper where the output need to be printed. Their speed varies from 200 to 2000 lines per minutes depending on the type of printing properties.Non-Impact Printers
Non-impact printers are usually faster that impact printers and work very quietly. They do not use a striking device to produce characters on the paper. Some of the popular non-impact printers are:Inkjet Printer
The most common type of printer for home uses in ColorInk Jet Printer. These printers form the image of the page by spraying small droplets of ink from the print head. The printer needs several colors of but the cost of consumables makes them costly to operate in the long run.
Laser Printer
A laser printer produces good quality images for office and business purposes. A drum coated with photosensitive material is charged, and then an image is written onto it by a laser or LED. The drum then rolls through the toner and the toner is then deposited onto the paper, and then fused into the paper with heat.
Most laser printers are monochrome (one color-black only) but more expensive laser printers with multiple color toner cartridges produce multi-color output. These printers are faster that ink jet printers; their speed is measured in pages per minute (PPM).
Thermal Printer
It uses heat elements to produce output on specail papers. themost common use is in printing slips by ATMs. Heat sensitive paper is used. Printing cost is high and hence is being used for only professional arts and design works purpose.Plotter
Plotters are used to print high quality vector graphics (engineering drawings, building plans, circuit diagrams etc.) under the control of computer. They use link pens or inkjet to draw graphics or drawings. They are generally Drum Plotter and Flat Bed Pltter.Speaker
It's a part of the multimedia computer. Speakers contain amplifiers which vibrate to produce the soundand gives audio output.Multimedia Projector
To project the computer output to a large number of people, Multimedia Projectors are used. It is widely used for showing presentations inside corporation during team meeting.
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