Computer have made great in roads. Computers play a major role in all spheres of our life and are used in variety of applications: In process automation, education, medicines, research and development, business, banking, product design, space technology, communication, transport, legal system, metrology etc.
A system is a machine which is capable of performing high speed calculations and logical operations. It can also store and retrieve information instantly. It can accept input in a prescribed form, process it and give the results of the processing in a specified format as an output, using a set of instructions called ‘program’.
Evolution of computers
1. The ABACUS - The first calculating machine and earliest known computing device is ABACUS. It has beads or marbles strewn together in a wooden frame with a divider bar. The addition or subtraction is carried out by moving the beads or marbles.
2. The Slide Rule - Later, the slide rule, an analog device was invented by William Oughtred, an English mathematician. It represents numbers by length and uses the concept of logarithms.
3. Pascal’s calculating machine (Pascaline) - In 1641, the French Mathematicians Blaise Pascal, invented a mechanical calculating machine. It was called pascaline. It consists of dials and toothed wheels. In order to carry out addition/subtraction operation, the numbers to be added/subtracted are dialed and the result could be seen at a window. Due to his diversified interests, Pascal could not improve the Pascaline machine. Leibniz another great German mathematician incorporated multiplication and division operations and improved the performance of Pascaline.
4. Analytical Engine - In 1983, Charles Babbage, an English professor of mathematicians, proposed a calculating machine called Analytical Engine. This machine contained many of the concepts of present’s day computers. If developed, the machine would have taken an input, would have a storage unit, would have performed the arithmetic operations and would have given a printout of the results. Hence, for this pioneering work, Charles Babbage is known as the father of the computers. Ada Augusta Byron, daughter of the famous English poet Lord Byron, helped Babbage in his work. She is infarct considered to be the world’s first, computer programmer. ‘The programming language ADA, has been developed in her honor.
5. Punched card - Dr. Herman Hollerith, an American statistician, used punched cards for tabulating and calculating data that was collected during the census.
6. Mark-I computer - The Harvard professor, Howard Aiken developed the first electromechanical computer. Mark-I computer was a huge machine occupying several rooms. Electromechanical relays and mechanical counters were used to carry out arithmetic calculations.
7. Atanasoff-Berry computer (ABC) - Dr. John Vincent Atanasoff, professor of physics and mathematicians from Iowa state college developed the first electronic computer and called it Atanasoff Berry computer (ABC). In this computer vacuum tubes were used as storage devices.
8. Electronic Numerical Integrator and Calculator (ENIAC) - The ENIAC was built by John Mauchly. It could perform 300 multiplications per second and was the fastest machine at the time of its development. The external plug boards or switches were used to give instructions to the computer.
In 1945, von Neumann used binary numbering system for the computers in place of decimal systems.
9. Electronic delayed storage Automatic Computer (EDSAC) and Electronic Discrete Variable Automatic Computer (EDVAC)- The EDVAC and EDSAC computers used the concept of stored program developed by Coldstine, Burks and Von Neumann. These computers were also called stored programs computers. A punched paper tape was used to store the computer program.
10. UNIVersal Automatic Computer (UNIVAC) - The UNIVAC was developed by Eckert and Mauchly magnetic tapes were used for data input and output operations.
11. Generation of computers-
The first generation computer (ENIC, EDVAC, EDSAC, UNIVAC) were bulky and occupied lot of space. They were built up of vacuum tubes. Hey produced lot of heat and there were frequent breakdowns or faults.
The second generation computer (IBM 1401) used transistors in place of vacuum tubes. The relays were replaced by magnetic core storage device. The drawbacks in the first generation computers namely, large size and frequent failures and large heat generation are alleviated in the second generation computers. The second generation computers were compact in size and consumed less power. The sped of operations is also increased.
The third generation computers (IBM 360, 370 series) were characterized by the use of integrated solid state circuiting, new inputs and output devices and improved storage devices. These computers became very compact in size. The arithmetic and Logic operations were carried out in milliseconds.
The fourth generation computer made use of Large Scale Integration (LSI) and Very Large Scale Integration (VLSI) based chips. This led to the development of microprocessor based minicomputers and microcomputers.
The fifth generation computers provided advanced hardware with higher speeds and higher storage capacities. They incorporate artificial intelligence and expert systems. The other features include, use of new computer languages, advancement in man-machine communication, input/output devices incorporating speech recognition and recognition of handwritten characters etc.
A digital computer in its simplest form is a fast electronic calculating machine that accepts digitized information from the user, processes it according to a sequence of instructions stored in the internal storage, and provides the processed information to the user. The sequence of instructions stored in the internal storage is called computer program and internal storage is called computer memory.
According to the size, cost computational power and application computers are classified as:
1. Microcomputers
2. Minicomputers
3. Desktop computers
4. Personal computers
5. Portable computers
6. Workstations
7. Mainframes or Enterprise systems
8. Servers
9. Super computers
1. Micro computers: As the name implies micro-computers are smaller computers contains only one Central Processing Unit. One distinguishing features of Microcomputer is that the CPU is usually a single integrated circuit called Microprocessor. Microcomputer is the integration of microprocessor and supporting peripheral (memory and I/O devices). The word length depends on the microprocessor used and is in the range of 8 bits to 32 bits. These types of computers are used for small industrial control, process control and where storage and speed requirements moderate.
2. Minicomputer: Minicomputers are the scaled up version of the microcomputer with the moderate speed and storage capacity. These are designed to process smaller data words, typically 32-bit words. This type of computers is used for scientific calculation, research, data processing application and many others.
3. Desktop computers: These computers are the computer which is usually found on a home or office desk. They consist of processing unit, storage unit, visual display an audio as output units, and keyboard and mouse as input units. Usually storage unit of such computer consists of hard disks, CD-ROM, and diskettes.
4. Personal computers: The personal computers are the most common form desktops computers.. They found wide use in homes, schools and business offices.
5. Portable Notebook computer: Portable notebook computer are the compact version of personal computers. The laptop computers are the good examples portable notebook computers
6. Workstations: Workstations have higher computation power than personal computers. They have high resolution graphics terminals and improved input/output capabilities. Workstations are used in engineering applications and in interactive graphics applications.
7. Mainframes or Enterprise systems: Mainframe computers are implemented using two or more central processing units (CPU). These are designed to work at very high speeds with large data word lengths, typically 64 bits or greater. The data storage capacity of these computers is very high. This type of computers are used for complex scientific calculations, large data processing applications, military defence control and for complex graphics applications (e.g. : For creating walk through with the help of animation software).
8. Servers: These computers have large storage unit and faster communication links. The large storage unit allows storing sizable database and fast communication links allow faster communication of data blocks with computers connected in the network. This computer serves major role in internet communication.
9. Supercomputers: These computers are basically multiprocessors computers used for the large-scale numerical calculations required in applications such as weather forecasting, robotics engineering, aircraft design and simulation.
The basic function of computer is to execute program, sequence of instructions. These instructions are stored in the computer memory. The instructions are executed to process data which already loads in to computer memory through input unit. After processing the data, the result is either stored back in to the computer memory for further reference or it is sent to the outside world through the output port.
The computer consists of five functionally independent units:
1. Input
2. Memory
3. Arithmetic and logic
4. Output
5. Control unit
Therefore, all functional units of the computer contribute to execute a program. Let us summarize the functions of different computer units.
The input unit accepts the digital information from user with the help of input devices such as keyboard, mouse, microphone etc. The input unit accepts data and instructions from the outside world to machine. It is operated by control unit. The information received from the input unit is either stored in the memory for later use or immediately used by the arithmetic and logic unit to perform the desired operations. The program stored in the memory decides the processing steps and the processed output are sent to the user with the help of output devices or it is stored in the memory for later reference. The memory unit stores both, data and instructions. All the above mentioned activities are coordinated and controlled by the control unit. The arithmetic-logic unit performs arithmetic and logical operations. The control unit transmits final results and messages to the outside world.
The arithmetic and logic unit in conjunction with control unit is commonly called central processing unit (CPU). Let us discuss the functional units in details.
1. Input Unit
A computer accepts digitally coded information through input unit using input devices. The most commonly used input devices are keyboard and mouse. The keyboard is used to position the screen cursor and therefore enter the information by selecting option. Apart from keyboard and mouse there are many other input devices are available, which include joysticks, trackball, space ball, digitizers and scanner.
2. Memory Unit
The memory unit is used to store programs and data. Usually, two type’s memory devices are used to form a memory unit: Primary memory device and Secondary storage memory device. The primary storage, commonly called main memory is a fast memory used for the storage of programs and active data (the data currently in process). The main memory is a semiconductor memory. It consists of large number of semiconductor storage cells, each capable of storing one bit information. These cells are read or written by central processing unit in a group of fixed size called word. The main memory is organized such that the contents of one word, containing n bits, can be stored or retrieved in one write or read operation, respectively.
To access data from a particular word from main memory each word in the main memory has a distinct address. This allows accessing any word from the main memory by specifying corresponding address. The number of bits in each word is referred as the word length of the computer. Typically, the word length varies from 8 to 64 bits. The number of such words in the main memory decides the size of memory or capacity of the memory. This is one of the specifications of the computer. The size of computer main memory varies from few million words to tens of millions words.
An important characteristic of a memory is an access time (the time required to access one word). The access time for main memory should be as small as possible. Typically, it is of the order of 10 to 100 nanoseconds. This access time also depends on the type of memory. In randomly accessed memories (RAMs), fixed time is required to access any word in the memory. However, in sequential access memories this time is not fixed.
The main memory consists of only randomly accesses memories. These memories are fast but they are small in capacitates and expensive. Therefore, the computer uses the secondary memories such as magnetic tapes, magnetic disks for the storage of large amount of data.
3. Arithmetic and Logic Unit
The arithmetic and Logic unit (ALU) is responsible for performing arithmetic operations such as add, subtract, division and subtraction, and logical operations such as ANDing, ORing, Inverting etc. To perform these operation operands from the main memory are brought in to the high speed storage elements called registers of the processor. Each register can store one word of data and they are used to store frequently used operands. The access times to registers are typically 5 to 10 times faster than access time to memory. After performing operation, the result is either stored in the register or memory location.
4. Output Unit
The output unit sends the processed results to the user using output devices such as video monitor, printer, plotter, etc. The video monitors display the output on the CRT screen whereas printers and plotters give the hard-copy output. Printers are classified according to their printing methodology: Impact Printers and non-impact printers. Impact printer’s press formed character faces against inked printers. Non impact printers and plotters use laser techniques, inkjet sprays, xerographic processes, electrostatic methods, and electro thermal methods to get images on to the paper. An inkjet printer is the example of non-impact printers.
5. Control Unit
As mentioned earlier, the control unit coordinated and control the activities amongst the functional units. The basic function of control unit is to fetch the instructions stored in the main memory, identify the operations and the devices involved in it, accordingly generate control signals to execute the devices involved in it, and accordingly generate control signals to execute the desired operations.
The control unit uses control signals or timing signals to determine when a given action is to take place. It controls input and output operations, data transfer between the processor, memory and input/output devices using timing signals.
The control and the arithmetic and logic unit of a computer are usually many times faster other devices connected to a computer system. This enables them to control a number of external input/output devices.
If you here 32GB USB drive is 200 rupees, 16GB USB drive is 100 rupees and 8GB USB is 50rupees. then don't bother them. Because in such drives most of them won't work properly and some won't work at all. We need to know that such kind of drves are not been released by the companies.We should keep this point in our mind. The Pen drive which they sell in electronic shopes, they may cheat us. Delhi cop have found these 454 duplicate USB's , memory cards in four shops in their enquiry. So how to find these duplicate memory cards and pendrives. Let see now.
1. If we scratch the company logo on the pen drive ,then if the logo got removed then it is duplicate. because the company logo on original pendrive will not get scratched and removed.
2. Compare to the original pendrives, the duplicate pendrives will be light in weight and the cheap plastic is used.
3. If we examine the pen drive, the company package of the fake drive will not look as a company product. It will look as if it is made in home.
4. Before purchasing the pen drive, we should check the pendrive by connecting to computer. when we connect the pen drive to the computer then it will show the company name tray. and immediately the drive will be installed.Then goto my computer and the drive which you find new there .Right click on that and then click on format.Now click on quick formate and formate it with start. Now again right click on the drive and then goto properties and check used space and free space.For example, if we purchase 4 GB drive then 3.74 GB is free space.
5.Copy any data in the pendrive. and then open the data in the pendrive.In duplicate pendrives, the data gets copied but it wont open in the pendrive and it shows corrupted error in red color.
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