INPUT AND OUTPUT DEVICES

Keyboard

 

The most common input device is the keyboard, which is basically the same the mechanical typewriter keyboard in that it has keys for printing upper and lower case letters, numbers and a variety of symbols.

 

However, since it is used to print out more than just letters and numbers, it needs to have extra keys to perform these additional actions.

 

The central section of the keyboard is the same as that of a mechanical typewriter; the numbers on the top row of keys and the letters and space bar below, all correspond exactly. Some of the punctuation marks above and around these keys are also the same although. as there is no standard layout for computer keyboards, each model has different combinations of symbols on each key.

 

Mouse

 

A mouse is a pointing device and is a excellent complement to the keyboard as an input device. The current trend in DOS and OS/2 operating systems towards ‘graphical user interfaces’ (GUI) has increased the popularity of the mouse. A graphical user interface is an operating environment that allows you to point onto screen pictures and buttons rather than keying in commands. A mouse is designed to be gripped in your hand and rotating one or more buttons on the top, which are used to select items and choose commands. A mouse is connected to the computer by a cable.

 

Trackball

 

A trackball is a pointing device that uses a sphere located on top that is rotated by hand to control cursor movement. Trackball are use for more precise movement than the mouse because of the user fingertip control over the sphere. The growing us of laptop and notebook computers has spurred the development of mini trackballs that are either attach easily to the side of these computers or are built into the keyboard.

 

Light Pen

 

A light pen is a pointing device that looks like a magic wand attached to the computer by a cable. It is use to select an item or commands from the screen by touching the screen surface. A light pen does not emit light but rather it contains sensors that send a signal back to the computer whenever they detect light. When light is detected, the computer determines the position of the electron beam at that time and ascertains the light pen’s location on the screen.

 

Joystick

 

A joystick is a pointing device that uses a lever to control the position of the cursor. It internally translates the position and speed of the lever into digital signal that are sent to the computer to control the cursor or others object on screen. Joysticks usually have one or more buttons located on the base or stem that are to control various software features.

 

Touch Screen

 

A touch screen recognizes the location of a contact on the screen through a build in grid of sensing lines or a grid of infrared beams and sensors. Many applications such as information dispensing booth uses touch screens because they offer an easy way for users to interact with the computer.

 

Speech Recognition

 

Probably the easiest way to input commands and data into the computer would be to speak to them. The ability to accept input by understanding the speech of a user is called speech recognition or voice recognition. Speech input is also valuable for individuals who have lost some or all of their eyesight or functional use of their hands.

 

OUTPUT DEVICES

 

 

Output is the process of translating data that are in machine-readable form into the form understandable to humans. Output device is the hardware that enables a computer to communicate information to humans. Hard copy is output that can be read immediately such as printer printouts. It is relatively stable and permanent form of output. Soft copy is a temporary form of output (E.g. text displayed on a computer screen, it is lost when the computer is turned off.)

 

Visual Display Unit (VDU)

 

Visual Display Unit (VDU) is a device which receives data via the computer keyboard. The screen or Cathode Ray Tube (CRT) displays the characters held in the VDU’s character store using an adapter card. The term VDU terminal is used to describe a screen and keyboard linked to a processor.

 

Screen size varies considerably, but may be typically 8 inches by 10 inches wide providing 40 or 80 characters per line and 20 to 25 lines. For a 2000 character display, there is also considerable variety in the format and size of displayed characters, for example, a typical character may be 0.1 inches wide and 0.2 inches high. Brightness and contrast controls are usually provided to enable the operator to adjust the image intensity.

 

A blinking (flashing) field facility is available on same terminals which can be used to draw the user’s attention to a field. Other terminals offer different image intensity, a reverse negative effect, or a different character font to identify selected fields.

 

When simple text based applications were the norm, most VDU screens used the Monochrome Display Adapter (MDA). These were high resolution monochrome screens initially in green, but now also in amber and black and white.

 

Color screens using the Color Graphics Adapter (CGA) gave poorer resolution and were initially only used for games. There were limited to four colors. The Enhanced Graphics Array (EGA) gave better resolution and made 16 colors available.

 

The most popular VDU uses the Video Graphic Array (VGA) standards. These give high resolution and make 256 colors available. These are particularly essential when running graphic software. Many manufacturers offer enhanced versions of VGA, either XVGA (extended) or SVGA (super). VGA screens use an analogue signal which converts the digital information into different voltage levels. This varies the brightness of the pixel.

 

Cathode Ray Tube (CRT)

 

The Cathode Ray Tube (CRT) of the VDU operates much like that in a television set. Electron guns (One in a monochrome screen, three in a color screen) send beams of electrons to trace a regular pattern of horizontal lines on the prosphar that coats the screen surface. Screen images are produced by varying the intensity of the beam. The beam scans the entire screen dozens of times each second. A color CRT system uses three electron guns to scans dots or strips of red, green, and blue phosphor that coat the screen’s surface.

 

Liquid Crystal Display (LCD)

 

Modern laptop computers use Liquid Crystal Display (LCDs) similar to those used in calculators and watches. The screen contains a layer of liquid crystal cells. Varying electrical charges are applied to some of the cells to produce the image.

 

PRINTERS

 

Printer is an output device that produces output on paper in the form of text or graphics and uses either impact or non-impact printing mechanisms. A character printers print one character at a time and can print up to several hundred characters per second (CPS).  It may print in unidirectional or bi-direction and this significantly increases print speed. Line Printer prints a line at a time and it can print up to few hundreds or a few thousand lines per minute.  These are used with large computer system. Page printer produces an entire page at a time. The fastest page printer can print up to few thousand pages per minute.  Paper can move through a printer either as continuous connected sheets or as single sheet some printers allow both methods.  Most printers have a carriage width that accepts 8.5 inches wide paper on which 80 characters can be printed.  Some uses paper that is 14 inches wide and 132 characters of normal size are printed on a line.

 

Impact printer

 

An impact printer produces characters when a ‘hammer’ or pin strikes an ink ribbon, which in turn presses against a sheet of paper and leaves an impression of the character on the paper. Commonly used impact printers used with microcomputers are dot matrix and daisy wheel printer. All impact printers can produce carbon copies.

 

Non-Impact printer

 

A non-impact printer does not strike to produce characters but they use technologies such as ink spraying which by nature are much quieter (e.g. ink-jet printer and laser printer)

 

TYPES OF PRINTERS

 

Dot Matrix Printer

 

Users print heads containing 9 or 24 pins. The 24-pin printer produces more dots than 9 pins resulting in much clearer characters. 9 pin printers usually produce compress print, standard quality and near letter quality print. Most 24-pin printers have letter quality, NLQ, standard and draft modes. These printers have speed between 100 to 600 cps. They are usually noisy while printing and are relatively inexpensive costing RM350 and above.

 

Dot matrix printers are likely to survive the market changes in technology, due to their application as impact printers. This means that they are able to print on multipart paper, which is used extensively in the accounting and auditing sector, and other businesses that need to keep accurate records and legal copies of documents.

 

Ink Jet Printer

 

Inkjet printers have recently taken over the cheaper end of the printer market. They have the benefit over dot matrix printers in providing a higher resolution of print, with a much quieter action. It is a non-impact printer that forms character by spraying ink from tiny nozzles in the print head. The ink is absorbed into the paper and when dried is permanently bonded to the paper. Ink jet produces high quality output quite comparable to that of a laser printer.

 

Laser Printer

 

Is non-impact printer that produces images on paper by directing a laser beam at a mirror that bounces the beam onto a drum. The laser leaves a negative charge on the drum to which positively charged black toner powder sticks. As paper rolls by the drum, the toner is transferred to the paper. A hot roller then bonds the toner to the paper. A laser printer internal memory stores a page at a time. When the entire page is loaded, it is printed. Desktop laser printers typically print a few pages (4 to 12 per minute). Laser printers are quiet and provide high quality text and images.

 

PLOTTERS

 

The growth of computer aided design and drafting (CADD) technology created demand for devices that produce high quality graphics in multiple colors on hard copy. A plotter is an output device the reproduces graphics image on paper using a pen that is attached to a moveable arm. The pen is directed across the surface of a stationary piece of paper. Many plotters combined moveable pen arm with a mechanism that rolls the paper back and forth to make the drawing. The two way movement allows the plotter to draw any configuration. Plotter applications are not limited to CADD. High quality bar graphs and pie charts created with a plotter can enhance business presentation too.

 

Voice Output

 

Voice output is another type of soft copy output where a computer uses a voice, e.g. in automobile warning systems, systems for the blind and in toys.  Speech coding is a type of voice output where it has large storage of human sounds. You may have heard in lift in modern days building. On the other hand, voice synthesis is the process of electronically reproducing the human voice in recognizable patterns.

 

SPECIAL PURPOSE INPUT DEVICES

 

 

Magnetic Ink Character Reader (MICR)

 

MICR is the method by which a computer recognizes characters which printed using special magnetic ink. The MICR reader first determines the shape of the character by sensing the magnetic charge in the ink. The shapes which can also be read by humans are than matched to a stored set of characters shape and converted into computer text, (E.g. Bank cheque)

 

Magnetic strips

 

Magnetic strips are thin bands of magnetically encoded data found on backs of many credit cards and automated teller cards (ATM). The data stored often include account number or special access codes. Magnetic strips cards are use to limit access to high security areas. To enter or secured area, a person inserts the card into a computerized read device. If the card contains the right code, the door automatically opens. Because no one can see or interpret the data by looking at the card, the data can be highly sensitive or personal.

 

Optical Mark Recognition (OMR)

 

OMR uses mark sensing to scan or translate the location of series of pen or pencil marks into computer readable form. Common use of OMR is to score test results.

 

Optical Bar Recognition (OBR)

 

OBR involves scanning of bar code into digital signals to be used by the computer. A bar code is composed of a set of vertical lines of varying widths and may also include number and letters. An input devices called optical bar reader is used to read the bar codes.

 

Optical Scanner

 

An optical scanner is an input device that uses light to sense the patterns of black and white on color on paper and convert them into digital signal that can be manipulated by graphical software. The scanning process begins by shinning a light on the material to be scanned. White areas reflected the light and black areas absorb it. The amount of lights the page absorbs or reflects help determine what is on the page. The quality determines by the number of dots per inch (dpi) and this is referred to as resolution. The higher the resolution, the better the quality of the image. Scanners are divided into Flatbed scanners and handheld scanners.

 

INPUT/OUTPUT DEVICES

 

 

Modem

 

We use a modem to connect PCs to the ordinary telephone networks: the Public Switched Telephone Network or PSTN. The telephone network operates using analogue voice signals over the last part of the network that connects a building to the exchange – sometimes called the local loop

 

A modem is a bridge between digital and analogue signals, and therefore provides an interface between computer (digital) and telephone (analogue) systems.

The modem converts on and off digital data into an analogue signal by varying, or modulating, the phase and frequency of an electronic wave. On a receiving end of a phone connection, a modem does just the opposite; it demodulates the analogue signals back into digital code. These two terms MOdulate and DEModulate give the modem its name.

 

PC PORTS

 

 

Ports are plug-like connectors found at the back of a computer. This is to enable the computer to communicate with peripheral devices such as printers and mouse. The cable that links the device to the computer is called an interface cable.

 

Serial Port

 

Transmit signals over one wire one bit at a time and has two way communication capabilities. Peripheral devices linked to serial port are such as serial printer and scanner. Serial ports have male connector and are also known as COM ports or RS-232 ports. Two types of serial ports found on IBM and compatible are DB-25 and DB-9 that has 25 and 9 pin respectively.

 

Parallel port

 

Transmit signal over 8 wires 8 bits at a time. Parallel ports are also known as printer port because they are used to connect the computer to the printer. A parallel port can be identified by the 25-pin female connector. A parallel connection has one disadvantage. The voltage changes in all the lines creates cross talk, a condition in which the signals leak from one line to another. Cross talk becomes worse the longer a parallel cable is – limiting the length of most parallel connections to 3 meters.

 

Universal Serial Bus (USB)

 

This is a relatively new form of connector. It utilizes a rectangular plug providing a high-speed serial connection. This is only part of the advantage however; much more important to most PC owners is the fact that USB devices can be plugged together without worrying about setting them up in any way. New equipment can be plugged in any time, even when the computer is running. A further advantage of USB is that it can be used to supply power to peripherals, thus eliminating a lot of cable clutter.

 

DEVICE DRIVERS

 

 

A device driver is software that allows peripheral devices to communicate with your computer. Examples of devices that require device driver include printer, mouse and monitor. Many DOS programs require the user to install software files that make up the device driver. Some program installs them automatically.

 

A printer driver tells the computer what kind of printer it will be working with and what type of printing capabilities the printer has e.g. font and points size. When ready to print, the driver converts them into a series of codes the printer understands. Laser printers and other types of printers use a set of codes known as the PDL (Page Description Language). PDL dictates character size font style, line spacing and other features. Two most famous PDLs are Adobe PostScript and Hewlett-Packard’s PCL (Printer Control Language)

 

A mouse driver enable a program to use a mouse e.g. MS Windows. The driver comes with the mouse instead of with the application program. The mouse drive is installed on the hard disk and must be loaded into memory each time the computer is turned on.