Computer is an electronic device which accepts data as input, performs processing on the data, and gives the desired output. A computer may be analog or digital computer.
Speed, accuracy, diligence, storage capability and versatility are the main characteristics of computer.
The computing devices have evolved from simple mechanical machines, like ABACUS, Napier’s bones, Slide Rule, Pascal’s Adding and Subtraction Machine, Leibniz’s Multiplication and Dividing Machine, Jacquard Punched Card System, Babbage’s Analytical Engine and Hollerith’s Tabulating Machine, to the first electronic computer.
Charles Babbage is called the father of computer.
The evolution of computers to their present state is divided intofive generations of computers, based on the hardware and software they use, their physical appearance and their computing characteristics.
First generation computers were vacuum tubes based machines. These were large in size, expensive to operate and instructions were written in machine language. Their computation time was in milliseconds.
Second generation computers were transistor based machines. They used the stored program concept. Programs were written in assembly language. They were smaller in size, less expensive and required less maintenance than the first generation computers. The computation time was in microseconds.
Third generation computers were characterized by the use of IC. They consumed less power and required low maintenance compared to their predecessors. High-level languages were used for programming. The computation time was in nanoseconds. These computers were produced commercially.
Fourth generation computers used microprocessors which were designed using the LSI and VLSI technology. The computers became small, portable, reliable and cheap. The computation time is in picoseconds. They became available both to the home user and for commercial use.
Fifth generation computers are capable of learning and self organization. These computers use SLSI chips and have large memory requirements. They use parallel processing and are based on AI. The fifth generation computers are still being developed.
Computers are broadly classified as microcomputers, minicomputers, mainframe computers, and supercomputers, based on their sizes and types.
Microcomputers are small, low-cost stand-alone machines. Microcomputers include desktop computers, notebook computers or laptop, netbooks, tablet computer, handheld computer and smart phones.
Minicomputers are high processing speed machines having more storage capacity than the microcomputers. Minicomputers can support 4-200 users simultaneously.
Mainframe computers are multi-user, multi-programming and high performance computers. They have very high speed, very large storage capacity and can handle large workloads. Mainframe computers are generally used in centralized databases.
Supercomputers are the most expensive machines, having high processing speed capable of performing trillions of calculations per second. The speed of a supercomputer is measured in FLOPS. Supercomputers find applications in computing-intensive tasks.
Computer is an electronic device based on the input-process-output concept. Input/Output Unit, CPU and Memory unit are the three main components of computer.
Input/Output Unit consists of the Input unit which accepts data from the user and the Output unit that provides the processed data. CPU processes the input data, and, controls, coordinates and supervises the operations of the computer. CPU consists of ALU, CU and Registers. The memory unit stores programs, data and output, temporarily, during the processing. Additionally, storage unit or secondary memory is used for the storing of programs, data and output permanently.
Computers are used in various areas of our life. Education, entertainment, sports, advertising, medicine, science and engineering, government, office and home are some of theapplication areas of the computers.
Bit is the smallest unit that is used to represent data in a computer. Byte is a group of 8 bits. One byte is the smallest unit of data that can be handled by the computer.
Memory is characterizedon the basis of its capacity and access time. The computer organizes its memory hierarchically so as to give the fastest speed and largest capacity of memory.
Memory is fundamentally of two types—Internal memory and External memory.
Internal memory has limited storage capacity, provides temporary storage, has fast access, the data and instructions stored in it are used by the CPU during execution, and is more expensive than secondary memory. Registers, cache memory, and primary memory constitute the internal memory. RAM and ROM are the two kinds of primary memory.
External memory or Secondary memoryhave very high storage capacity, are non-volatile unless erased by user, have slow access, store the data and instructions that are not currently being used by CPU, and are cheapest among all memory. Magnetic disk and optical disk are storage devices.
Organization of memory with respect to the CPU, is as follows—registers are placed inside CPU, cache memory is placed inside CPU, primary memory is placed next in the hierarchy, and secondary memory is the farthest from CPU.
Registers are very high-speed storage areas located inside the CPU. Registers are manipulated directly by the control unit of the CPU during instruction execution.
Cache, the fast memory, is placed between the CPU and the RAM. The contents from the RAM are stored in the cache.
RAM stores data and instructions during the operation of computer. RAM is a random access volatile memory having limited size due to its high cost. RAM affects the speed and power of the computer.
RAM memory chipsare of two types—DRAM and SRAM. DRAM is used as main memory as it is small and cheap. SRAM chip is used in cache memory due to its high speed.
ROM is a non-volatile primary memory which stores the data needed for the start up of the computer. Instructions to initialize different devices attached to computer and the bootstrap loader are stored in ROM. PROM, EPROM and EEPROM are some of the ROMs.
Flash memory is a kind of semiconductor-based non-volatile, rewritable computer memory. It is used in digital camera, mobile phone, printer, laptop computer, and MP3 players.
Magnetic tapes are inexpensive, can store a large amount of data, are easy to transport, are slow access device, and are suitable for back-up storage.
Magnetic disks are cheap storage device, can store a large amount of data, are easy to carry, are suitable for frequently read/write data and are fast access device. Access time of disk is the sum of seek time, latency time and time for data transfer.
Floppy disk is a flat, round, single disk enclosed in a jacket. It is portable, small, inexpensive and slower to access than hard disk. It comes in two basic sizes—5-¼ inch and 3-½ inch.
Hard disk is a fixed disk and can store much more data than floppy disk. Hard disk is the key secondary storage device of computer.
Zip disk have the speed and capacity of hard disk and portability of floppy disk.
Optical disk consists of a single spiral track that starts from the edge to the centre of disk. It can store large amount of data in small space.
CD-ROM is an optical disk that can only be read and not written on. It has high-storage density and is a low-cost device compared to floppy disk and hard disk.
DVD-ROM is a high-density optical storage device which stores data on both sides of the disk. It is used to store a full-length movie.
Recordable optical disks are CD-R, CD-RW and DVD-R.
Computer uses its memory from the time you switch on the computer till you switch it off.
A user interacts with the computer viaInput-Output (I/O) devices. The peripheral devices are attached externally to the computer machine.
Input unit accepts input data from the user via input device, transforms the input data in computer acceptable form and provides the transformed input data for processing.
Output unit accepts output data from computer via output device, transforms the output information to human readable form and provides the transformed output to user.
Some devices are both input and output devices. Hard disk drive, floppy disk drive, optical disk drives are examples of input-output devices.
Keyboard is used to enter text data. Standard keyboard contains 101 keys to 110 keys.
Mouseis a small hand-held pointing input device used to enter data by pointing to a location on the computer monitor screen.
Trackball looks like an upside-down mouse and requires the ball to be rotated manually with a finger.
Joystick is a stick with its base attached to a flexible rubber sheath inside a plastic cover. It is used for playing video games.
Digitizing tablet has a flat bed tablet, and a pen with an electronic head which is moved on the tablet. Digitizing tablet is used for computer aided design of buildings, maps, etc.
Light pencontains a photocell in a small tube and is used to select objects directly on the computer screen.
Touch screen is a clear glass panel that is placed over the view area of the computer screen. The user uses the fingertip on the computer screen to select an option. It is used in ATMs.
Audio input devices use a microphone to input a person’s voice, a sound card to translate analog audio signals from microphone into digital codes and speech recognition to translate spoken words into text.
Video input is provided using video camera and digital camera. Computer vision is an area of computer science that deals with images.
Scanner is used to input data directly into the computer from the source document without copying and typing the data. A scanner can be a hand-held scanner or flat bed scanner.
OCR is a technique for the scanning of a printed page, translating it, and then using the OCR software to recognize the image as ASCII text that is editable.
MICR is used in banks to process large volumes of cheques. It is used to recognize the magnetic encoding numbers printed at the bottom of a cheque.
OMR uses an optical mark reader to detect marks on a paper. OMR is widely used to read answers of objective type tests, questionnaires, etc.
Barcodes are adjacent vertical lines of different width that are machine readable. Barcode reader reads the barcode. They are used to read labels in departmental stores and in libraries.
Printerprints the output onto a paper. Plotter is used for drawing maps, blueprints of ships, buildings, etc.
Impact printers are those in which the typeface strikes against the paper. Dot matrix printers, daisy wheel printers and drum printers are examples of impact printers.
Non-Impact printers do not hit or impact a ribbon to print. Ink-jet printers and laser printers are non-impact printers.
COMis a high-speed and low-cost process to record computer output directly from the computer tape on a microfilm. It is used to store manuals and for archiving of records.
Monitor is attached to the computer on which the output is displayed. The clarity of image on the computer screen depends on the resolution of screen, the dot pitch, and the refresh rate.
Screen image projectorsdisplay information from the computer onto a large white screen.
Audio output devicelike speakers, headset or headphone are used to output sound from the computer system.
I/O portsconnect the I/O devices to the computer. Serial and parallel ports, USB port and Firewire are some of the commonly used I/O ports.
I/O systemuses the I/O hardware (buses, ports, device controllers and I/O devices) and the I/O software (device drivers) for its working. Face value of a digit is the digit located at that place. The position value of digit is (baseposition). The number is the sum of (face value * baseposition) of all the digits.
In computer science, decimalnumber system (base 10), binary number system (base 2), octal number system (base 8), and hexadecimal number system (base 16) concern us.
Decimal number system has 10 digits—0 to 9, the maximum digit being 9.
Binary number system has two digits—0 and 1.
Octal number system consists of eight digits—0 to 7, the maximum digit being 7.
Hexadecimal number system has sixteen digits—0 to 9, A, B, C, D, E, F, where (A is for 10, B is for 11, C—12, D—13, E—14, F—15). The maximum digit is F, i.e., 15.
Conversion of octal or hexadecimal number to binaryor vice-versa uses the shortcut method. Three and four bits of a binary number correspond to an octal digit and hexadecimal digit, respectively.
Binary arithmetic operations are the binary addition, subtraction, multiplication and division operations performed on the binary numbers.
For any number in baser, there is r’s complement and r–1’s complement. For example, binary numbers can be represented in 1’s complement and 2’s complement.
Sign bit is the most significant bit. The sign bit is 1 and 0 for a positive number and negative number, respectively.
Position of binary pointin a binary number is represented using Fixed Point Number Representation and Floating Point Number Representation.
In fixed point representation, the positive integer binary number is represented with sign bit 0 and magnitude as positive binary number. The negative integer is represented in signed magnitude representation, signed 1’s complement representation and signed 2’s complement representation.
Addition of two signed binary numbersrequires the positive number to be represented as binary number and negative number to be represented in 2’s complement form.
Floating point representationhas two parts—Mantissa and Exponent. Mantissa is a signed fixed point number and exponent shows the position of the binary point in the mantissa.
Binary Coding schemesrepresent data in a binary form in the computer. ASCII, EBCDIC, and Unicode are the most commonly used binary coding scheme.
EBCDIC is a 8-bit code with 256 different representations of characters. It is mainly used in mainframe computers.
ASCII-8 is a 8-bit code and allows 256 characters to be represented. ASCII is widely to represent data in computers, internally.
Unicode is a universal character encoding standard for the representation of text in multi-lingual environments. UTF-8 is the most commonly used encoding.
Logic gate is the hardware electronic circuit that operates on input signals to produce output signal. AND, OR, NOT, NAND, NOR, XOR and XNOR are some of the logic gates