Characteristics of computers:
Computers of all sizes have common characteristics – speed, arithmetical and logical operations, accuracy, reliability, storage, retrieving data and programs, automation, versatility, communications, diligence, feelings, consistency and precision. Computers are the foundation of business, travel, and leisure life today. Computers provide the processing speed required by all facets of society. The quick service we expect at the bank, at the grocery store, on the stock exchange, and on the Internet are dependent on the speed of computers. Can you imagine our world without computers? Computers are extremely reliable as well. Most errors are caused by humans, not computers. Computers are capable of storing enormous
amounts of data that must be located and retrieved very quickly. The capability to store and retrieve volumes of data is at the core of the Information Age. Now-a-days computer is playing a main role in everyday life it has become the need of people just like television, telephone or other electronic devices at home. It solves the human problems very quickly as well as accurately. The important characteristics of a computer are
described below:

  1. Speed
    The computer is a very high speed electronic device. The operations on the data inside the computer are performed through electronic circuits according to the given instructions. The data and instructions flow along these circuits with high speed that is close to the speed of light. Computer can perform millions of billions of operations on the data in one second. The computer generates signals during the operation process therefore the speed of computer is usually measure in megahertz (MHz) or Giga hertz (GHz). It means million cycles units of frequency is hertz per second. Different computers have different speed.
  1. Arithmetical and Logical Operations
    A computer can perform arithmetical and logical operations. In arithmetic operations, it performs the addition, subtraction, multiplication and division on the numeric data. In logical operation it compares the numerical data as well as alphabetical data.
  2. Accuracy
    In addition to being very fast, computer is also very accurate device. It gives accurate output result provided that the correct input data and set of instructions are given to the computer. It means that output is totally depended on the given instructions and input data. If input data is in-correct then the resulting output will be in-correct. In computer terminology it is known as garbage-in garbage-out.
  3. Reliability
    The electronic components in modern computer have very low failure rate. The modern computer can perform very complicated calculations without creating any problem and produces consistent (reliable) results. In general, computers are very reliable. Many personal computers have never needed a service call. Communications are also very reliable and generally available whenever needed.
  4. Storage
    A computer has internal storage (memory) as well as external or secondary storage. In secondary storage, a large amount of data and programs (set of instructions) can be stored for future use. The stored data and programs are available any time for processing. Similarly information downloaded from the internet can be saved on the storage media.
  5. Retrieving data and programs
    The data and program stored on the storage media can be retrieved very quickly for further processing. It is also very important feature of a computer.
  6. Automation
    A computer can automatically perform operations without interfering the user during the operations. It controls automatically different devices attached with the computer. It executes automatically the program instructions one by one.
  1. Versatility
    Versatile means flexible. Modern computer can perform different kind of tasks one by one of simultaneously. It is the most important feature of computer. At one moment you are playing game on computer, the next moment you are composing and sending emails etc. In colleges and
    universities computers are used to deliver lectures to the students. The talent of computer is dependent on the software.
  2. Communications
    Today computer is mostly used to exchange messages or data through computer networks all over the world. For example the information can be received or send through the internet with the help of computer. It is most important feature of the modern information technology.
  3. Diligence
    A computer can continually work for hours without creating any error. It doesnot get tired while working after hours of work it performs the operations with the same accuracy as well as speed as the first one.
  4. Feelings
    Computer is an electronic machine. It has no feelings. It detects objects on the basis of instructions given to it. Based on our feelings, taste, knowledge and experience: we can make certain decisions judgments in our daily life. On the other hand, computer cannot make such judgments on their
    own. Their judgments are totally based on instructions given to them.
  5. Consistency
    People often have difficulty to repeat their instructions again and again. For example, a lecturer feels difficulty to repeat a same lecture in a class room again and again. Computer can repeat actions consistently (again and again) without losing its concentration:
     To run a spell checker (built into a word processor) for checking
    spellings in a document.
     To play multimedia animations for training purposes.
     To deliver a lecture through computer in a class room etc.
     A computer will carry out the activity with the same way every time.
     You can listen a lecture or perform any action again and again.
  1. Precision
    Computers are not only fast and consistent but they also perform operations very accurately and precisely. For example, in manual calculations and rounding fractional values (That is value with decimal point can change the actual result). In computer however, you can keep the accuracy and
    precision upto the level, you desire. The length calculations remain always accurate.
    1.5 Organization of a Computer
    A computer is a fast and accurate device, which can accept data, store data, process them and give, desired results as output. The computer is organized into four units such as, Input unit, CPU, Secondary memory and
    Output unit as shown in the following diagram.
1.5.1 Input Unit
Any device designed to assist in the entry of data into a computer is known as Input device. Input devices convert data from any convenient external format into binary codes that a computer can store and manipulate internally. Some of the most common, most popularly used devices are discussed below.
This Input device is categorized as a pointing device because it is used to point and select an option on the monitor. It is small boxlike object that is connected to the computer by a cable and can be rolled around on the table. A pointer on the screen follows the movements of the mouse; rolling the mouse left moves the pointer left by an equipment amount, rolling the mouse in the right direction moves the pointer in the right direction, rolling the mouse in the up direction moves the pointer in the up direction, rolling the mouse in the down direction moves the pointer in the down direction and you can roll the mouse in a angular direction also. In order to select an option on the computer screen, the user should move the pointer at the desired position and press the button on the mouse. The mouse can be
used to open menus, select texts for editing, move objects on the screen, draw images or diagrams etc.
A mouse can be classified on the basis of the number of buttons it has, the technology it uses, and the kind of interface it shares with the computer. A mouse may have one, two or three buttons. The program that uses the mouse determines the function of each button. A mouse may be classified as a Mechanical mouse and an Optical mouse, on the basis of the technology it uses. In a Mechanical mouse, the rubber-coated ball that

projects through the bottom surface rotates as the mouse is moved along a flat surface and sends electrical signals to the system unit by means of switches inside the mouse. This causes the cursor, or pointer, to move in a corresponding fashion. An Optical mouse uses diodes to emit light beam
instead of a rotating ball to detect movement across a specially patterned metal pad.

  1. Light Pen
This is also categorized into a pointing device, which can be used only with video displays. It can be used to select an option by simply pointing at it, or drawing figures directly on the screen. An electron beam that repeatedly scans the display screen from left to right and from top to bottom produce a
video display. Because of this scanning action, each point on the display is illuminated at a slightly different time.
The light pen, which is a pen like device, has a photo detector at its tip. The detector can detect changes in the brightness of the screen. The light pen is connected to the computer by a cable. When the pen is pointed at a particular spot on the screen, the point is scanned and the photo detector records changes in the brightness and sends electrical pulses to the computer. The computer can find out the exact spot with this information. Light pens are useful for menu-based applications. It is also useful for drawing graphics in Computer Aided Design software.

Touch Screen:

A type of display screen that has a touch-sensitive transparent panel covering the screen. Instead of using a pointing device such as a mouse or light pen, you can use your finger to point directly to objects on the screen. Although touch screens provide a natural interface for computer novices, they are unsatisfactory for most applications because the finger is such a relatively large object. It is impossible to point accurately to small areas of
the screen.

Joy Stick:

A lever that moves in all directions and controls the movement of a pointer or some other display symbol. A joystick is similar to a mouse, except that

with a mouse the cursor stops moving as soon as you stop moving the mouse. With a joystick, the pointer continues moving in the direction the joystick is pointing. To stop the pointer, you must return the joystick to its upright position. Most joysticks include two buttons called triggers. Joysticks
are used mostly for computer games, but they are also used occasionally for
CAD/CAM systems and other applications.

  1. Keyboard:
Keyboards are the most widely used input devices. The most popular keyboards are those that look, feel, and possibly sound like an ordinary typewriter keyboard. Alternatives are Membrane keyboards, whose keys are merely printed on a plastic membrane. A pressure sensitive two-dimensional keyboard covered with a dust proofed and dirt proofed plastic sheet are useful in dirty environments. Keyboards are of different varieties. Generally a keyboard has 105 keys. It features 12 function keys arranged at the top of
the keyboard, and larger Backspace key, a numeric keypad, a cursor movement keypad, toggle lights, Shift keys, Alt keys, Ctrl keys, Caps Lock key, Num Lock key, Spacebar key, Enter key, Alphabetical keys etc.
These are the eyes of your computer. They can see images or printed text and translate them into binary code. Most scanners collect data from a page by recording, which areas are light and which areas are dark. Th ey contain a camera, which is made up of thousands of tiny cells, called charge coupled devices (CCD). Each CCD detects whether a small part of the image is either light or dark. It transmits this data to the CPU, which then creates the image. Some scanners are sensitive enough to tell the difference between colors.
Many scanners available nowadays are capable of not only scanning texts and graphics, but also i ntegrated text and graphic files. Scanners are used to reproduce photographs on the computer screen. Businesses use scanners for storing documents on the computer. Optical Character Readers (OCR): These are another kind of input devices that are used to read any printed text. They can interpret handmade marks, handwritten characters, machine printed characters and special symbols and codes. Optical character readers scan text character-by-character converts them into machinereadable codes and store it in the memory. Since they read characters at the rate of around 2600 characters per second this reduces the organizations the data inputting time.
Magnetic Ink Character Reader (MICR):
A magnetic character reader system for reading and identifying magnetized characters printed on a document such as a check, in which analog waveforms derived from scanning the characters are analyzed by rectifying and integrating the waveform to generate a value representing the gain of a programmable gain amplifier for use in amplifying the waveform to compensate for variations in ink intensity. eans are provided for generating a value representing the center of gravity of the area under each peak of the amplified waveform for use in retiming the peak sampling windows for compensating for variations in the speed of the document past the magnetic read head. Digital values representing the area under each peak curve in the waveform are compared with corresponding values of a plurality of reference characters to identify the unknown character.
Bar Code Reader:
This is used to read different kind of vertical lines known as bars which signify some information.
Touch Pad
Most laptop computers today have a touch pad pointing device. You move the on-screen cursor by sliding your finger along the surface of the touch pad. The buttons are located below the pad, but most touch pads allow you to perform “mouse clicks” by tapping on the pad itself.
Touch pads have the advantage over mouse that they take up much less room to use. They have the advantage over trackballs (which were used on early laptops) that there are no moving parts to get dirty and result in jumpy
cursor control.
Track Point

Some sub-notebook computers (such as the IBM ThinkPad), which lack room for even a touch pad, incorporate a track point, a small rubber projection embedded between the keys of the keyboard. The track point acts like a little joystick that can be used to control the position of the on-screen cursor.
Graphics Tablet:

A graphics tablet consists of an electronic writing area and a special “pen” that works with it. Graphics tablets allow artists to create graphical images

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