Programmable machine. The two principal characteristics of a computer are: It responds to a specific set of instructions in a well-defined manner. It can execute a prerecorded list of instructions (a program). Modern computers are electronic and digital. The actual machinery -- wires, transistors, and circuits -- is called hardware; the instructions and data are called software All general-purpose computers require the following hardware components:1. Memory : Enables a computer to store , at least temporarily, data and programs.2. Mass Storage Device: Allows a computer to permanently retain large amounts of data. Common mass storage devices include disk drives and tape drives.3. Input Device: Usually a keyboard and mouse, the input device is the conduit through which data and instructions enter a computer.4. Output Device: A display screen, printer, or other device that lets you see what the computer has accomplished.5. Central Processing Unit (CPU): The heart of the computer, this is the component that actually executes instructions.
Computers can be generally classified by size and power as follows:1. Personal Computer : A small, single-user computer based on a microprocessor. In addition to the microprocessor, a personal computer has a keyboard for entering data, a monitor for displaying information, and a storage device for saving data.2. Workstation : A powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and a higher-quality monitor.3. Minicomputer : A multi-user computer capable of supporting from 10 to hundreds of users simultaneously.4. Mainframe : A powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.5. Supercomputer : An extremely fast computer that can perform hundreds of millions of instructions per second.
1. SpeedThe computer is a very high speed electronic device. The operations on the data inside the computer areperformed through electronic circuits according to the given instructions. The data and instructions flowalong these circuits with high speed that is close to the speed of light. Computer can perform million ofbillion of operations on the data in one second. The computer generates signals during the operationprocess therefore the speed of computer is usually measure in mega hertz (MHz) or giga hertz (GHz). Itmeans million cycles units of frequency is hertz per second. Different computers have different speed.2. Arithmetical and Logical OperationsA computer can perform arithmetical and logical operations. In arithmetic operations, it performs theaddition, subtraction, multiplication and division on the numeric data. In logical operation it compares thenumerical data as well as alphabetical data.3. AccuracyIn addition to being very fast, computer is also very accurate device. it gives accurate output result providedthat the correct input data and set of instructions are given to the computer. It means that output is totallydepended on the given instructions and input data. If input data is in-correct then the resulting output willbe in-correct. In computer terminology it is known as garbage-in garbage-out.4. ReliabilityThe electronic components in modern computer have very low failure rate. The modern computer canperform 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.
5. StorageA computer has internal storage (memory) as well as external or secondary storage. Insecondary storage, a large amount of data and programs (set of instructions) can be stored forfuture use. The stored data and programs are available any time for processing. Similarlyinformation downloaded from the internet can be saved on the storage media.6. Retrieving data and programsThe data and program stored on the storage media can be retrieved very quickly for furtherprocessing. It is also very important feature of a computer.7. AutomationA computer can automatically perform operations without interfering the user during theoperations. It controls automatically different devices attached with the computer. It executesautomatically the program instructions one by one.8. VersatilityVersatile means flexible. Modern computer can perform different kind of tasks one by one ofsimultaneously. It is the most important feature of computer. At one moment your are playinggame on computer, the next moment you are composing and sending emails etc. In colleges anduniversities computers are use to deliver lectures to the students. The talent of computer isdependent on the software.
9. CommunicationsToday computer is mostly used to exchange messages or data through computer networks allover the world. For example the information can be received or send through the internet withthe help of computer. It is most important feature of the modern information technology.10. DiligenceA computer can continually work for hours without creating any error. It does not get tired whileworking after hours of work it performs the operations with the same accuracy as well as speedas the first one.11. No FeelingsComputer is an electronic machine. It has no feelings. It detects objects on the basis ofinstructions given to it. Based on our feelings, taste, knowledge and experience: we can makecertain decisions and judgments in our daily life. On the other hand, computer can not makesuch judgments on their own. Their judgments are totally based on instructions given to them.
12. ConsistencyPeople often have difficulty to repeat their instructions again and again. For example, a lecturerfeels difficulty to repeat a same lecture in a class room again and again. Computer can repeatactions consistently (again and again) without loosing 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 orperform any action again and again.13. PrecisionComputers are not only fast and consistent but they also perform operations very accuratelyand precisely. For example, in manual calculations and rounding fractional values (That is valuewith decimal point can change the actual result). In computer however, you can keep theaccuracy and precision up to the level, you desire. The length calculations remain alwaysaccurate.
Input DevicesThe devices that are used to enter data and instructions into the computer are called input devices or units.In old computers the punched card readers, paper tape readers were used as input devices. Now-a-days themost commonly used input devices are Keyboard and Mouse.Output DevicesThe computer processes the given input data and gives the output. The devices that are used to get outputfrom a computer in readable from are called output devices. A number of output devices are available. Somecommonly used output devices are video display units (VDU) and printers.Central Processing UnitCentral Processing Unit is simply called as CPU. It is the main components of the computer and it is alsocalled the Processor. The processor used in microcomputer is referred to as Microprocessor. CPU isconsidered the brain of the computer. It performs all operations of data according to programs instructions.It executes the program instructions and tells other parts of the computer what to do. The CPU fetchesinstructions of program from main memory and executes them one by one. The CPU also has the ability todecide which instruction will be executed next. The speed of the CPU is measured in Mega Hertz (MHz) orGiga (or more).The CPU is divided into two main part of sub-units. These are:Control Unit (CU)Arithmetic Logic Unit (ALU)
1. Control Unit (CU)The control unit is the most important component of the CPU. It controls and coordinates theactivities of all the other units of the computer. The control unit is considered as the logical hub ofthe computer. It acts as a central nervous system for the other components of the computer.For example the control unit receives the data and instructions from the input device and storesthem in the main memory. It performs all these functions by issuing commands to the relevantunit of the computer.The control unit also controls the execution of instructions given to the computer. It fetches theinstructions and data from the memory unit. It decodes and executes the instructions one by one.2. Arithmetic Logic Unit (ALU)Arithmetic Logic Unit or simply ALU is another important component of CPU. It performs thearithmetic and logical operations on the data. When the control unit encounters and instructionrelated to perform arithmetic or logical operation on data, it passes that instruction to ALU.In arithmetic operations ALU performs the addition, subtraction, multiplication and division.In logical operations ALU compare the numerical data as well as alphabetic data. For example, itchecks whether first number is greater than second, less than second or equal to second etc. Itmust be noted that some of the logical operations can be done on test data. For example whenyou want to search a word in a document., the CPU matches each word of the document ent withthe given word. Actually the ALU compares each word of document with the given word throughrelational equal operator (=).The ALU consists of a number of registers and adder circuits. A register is a temporary storagedevice which holds data and instruction as long as it is being interpreted (decoded) and executed.When the data and instructions are fetched from main memory for processing, these have to bestored in one of the registers of the CPU.
Input is any data or instructions entered into the computer in the form of signals. The input into thecomputer can be entered:1. Through keyboard (by typing characters).2. By selecting commands (icons) on the screen and then clicking with mouse.3. By pressing finger on a touch screen.4. By speaking into a microphone.5. By sending image through digital camera.6. By scanning data printed on paper through scanner etc.Therefore, the devices that are used to enter data and instructions or commands into the computer arecalled input devices or units. The input devices are the eyes and ears of computers. In old computers thepunched card readers, paper tape readers were used as input devices. Now-a-days, the commonly usedinput devices are:1. Keyboard2. Mouse3. Touchpad4. Trackball5. Joystick6. Light Pen7. Digital Scanner8. Digital Camera9. Microphone
The keyboard is the most commonly used input device. It is used to feed data and instructions into acomputer. It is similar to an electric typewriter. A keyboard contains keys for each alphabeticcharacters, digits and special characters. The data and instructions are feed into the computer by pressingthe related keys on the keyboard. The keyboard having some additional keys for specific functions. Keyboardused with personal computer typically have from 101 to 105 keys.On laptop and many other handheld computers, the keyboard is built into the top of the system unit.Usually, these keyboards are smaller in size and have fewer keys such as 85 keys.Some old type computers have built-in keyboards. Now-a-days, the computer has a separate keyboard. It iseasily plugged in computer. A keyboard is connected to the serial or USB port on the system unit. A standardcomputer keyboard is also referred to as QWERTY keyboard. This name represents the first left most letterson the top alphabetic line of the keyboard spell. Some advanced keyboards do not require the cable toconnect with the cable. They enter data into the computer through wireless technologies such as radiowaves or infrared light waves. These type of keyboards are known as cordless or wireless keyboards.Keyboard’s may have USB or PS/2 wire portA keyboard may be divided into four area. There are:1. Alphanumeric keypad or typewriter area.2. Numeric keypad.3. Screen Navigation keys.4. Editing keys.5. Function keypad.
1. Alphanumeric KeypadThis area is like a typewrite, it is because this area of keyboard is referred to as Typewriter Area. The useruses this area to enter general information into the computer. Typists usually use this area of keyboard. Thisarea consists of:Alphabetic character keys "A" to "Z" and lower case letters "a" to "z".Numeric keys "0" to "9".Many other special keys like Spacebar, Enter key, Ctrl key etc.2. Numeric KeypadA set of numeric keys and arithmetic operator keys on the right of keyboard that are similar to calculatorkeys is referred to as Numeric Keypad. It also has an extra Enter key and Num Lock key. The Num Lock key isused to activate or deactivate the numeric keypad. The numeric keypad is mostly used for numeric dataentry.3. Screen Navigation KeysThe keys that are normally used in word processor or other application programs to move cursor into thedocument on the screen are referred to as navigation keys. The most important navigation keys are:Arrow Keys Used to move the cursor left, right, up and down on the screen. These are also referred to ascursor keys.Page Up Key Used to move the cursor one page up of document on the screen. Page Down Key Used to move the cursor one page down of document on the screen.End Key Used to move the cursor to the end of line or to end of screen or document.Home Key Used to move the cursor to the top left of screen on beginning of document.
4. Editing KeysThe keys that are normally used in word processor or other application programs for editing (modifying) thedocument are referred to as editing keys. The most important editing keys are:Delete Key Used to delete the characters towards the right of cursor position.Backspace Key Used to delete the characters from the current cursor position toward left.Enter Key Used to insert new line or paragraph into text editing programs. It is also used to enter selectedcommand into the computer.Tab Key Used to insert a tab.Caps Lock Key Used to change lowercase letters mode to uppercase and vice versa.Insert Key Used to change insert mode to overwrite mode and vice versa.5. Function KeysThere are 10 or 12 function keys on the top of keyboard that are labeled as F1, F2,........ F12. These keys arereferred to as Function Keys. These are used to perform special functions. The function of each key dependsupon the software being used on the computer. The designer of the software assigns these keys in hissoftware as shortcut commands or keys to perform specific task. For example, in most software the functionkey F1 is used to get online help about the software running on the computer.
Many keyboards also have a Windows Key. When Windows key is presses, Start Menu of Windows isdisplayed.The advanced keyboards also include buttons that allow the user to access the computers CD or DVD drive.Adjust speaker volume, open an e-mail program, start a web browser and search the Internet. Somekeyboards also provide the USB ports used to plug the USB device directly to the keyboard instead of systemunit
In computing, a mouse (plural mice, or mouse devices.) is a pointing device that functions by detecting two-dimensional motion relative to its supporting surface. Physically, a mouse consists of an object held underone of the users hands, with one or more buttons. It sometimes features other elements, such as "wheels",which allow the user to perform various system-dependent operations, or extra buttons or features can addmore control or dimensional input. The mouses motion typically translates into the motion of a cursor on adisplay, which allows for fine control of a Graphical User Interface.The name mouse, originated at the Stanford Research Institute, derives from the resemblance of earlymodels (which had a cord attached to the rear part of the device, suggesting the idea of a tail) to thecommon mouse.Some high-end mice have 16-bit wide data path. Some high-end mice come with gold-plated USB connector.
A light pen is a computer input device in the form of a light-sensitive wand used in conjunction with acomputers CRT TV set or monitor. It allows the user to point to displayed objects, or draw on the screen, ina similar way to a touch screen but with greater positional accuracy. A light pen can work with any CRT-based display, but not with LCD screens projectors and other display devices.A light pen is fairly simple to implement. Just like a light gun, a light pen works by sensing the sudden smallchange in brightness of a point on the screen when the electron gun refreshes that spot. By noting exactlywhere the scanning has reached at that moment, the X,Y position of the pen can be resolved. This is usuallyachieved by the light pen causing an interrupt, at which point the scan position can be read from a specialregister, or computed from a counter or timer. The pen position is updated on every refresh of the screen.
Trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation ofthe ball about two axes—like an upside-down mouse with an exposed protruding ball. The user rolls the ballwith the thumb, fingers, or the palm of the hand to move a cursor. Large tracker balls are common on CADworkstations for easy precision. Before the advent of the touchpad, small trackballs were common onportable computers, where there may be no desk space on which to run a mouse. Some small thumbballsclip onto the side of the keyboard and have integral buttons with the same function as mouse buttons
A joystick is an input device consisting of a stick that pivots on a base and reports its angle ordirection to the device it is controlling. Joysticks are often used to control video games, andusually have one or more push-buttons whose state can also be read by the computer. Apopular variation of the joystick used on modern video game consoles is the analog stick.The joystick has been the principal flight control in the cockpit of many aircraft, particularlymilitary fast jets, where center stick or side-stick location may be employed.Joysticks are also used for controlling machines such as cranes, trucks, underwater unmannedvehicles, wheelchairs, surveillance cameras and zero turning radius lawn mowers. Miniaturefinger-operated joysticks have been adopted as input devices for smaller electronic equipmentsuch as mobile phones.
In computing, a scanner is a device that optically scans images, printed text, handwriting, or an object, andconverts it to a digital image. Common examples found in offices are variations of the desktop (or flatbed)scanner where the document is placed on a glass window for scanning. Hand-held scanners, where thedevice is moved by hand, have evolved from text scanning "wands" to 3D scanners used for industrial design,reverse engineering, test and measurement, orthotics, gaming and other applications. Mechanically drivenscanners that move the document are typically used for large-format documents, where a flatbed designwould be impractical.Modern scanners typically use a charge-coupled device (CCD) or a Contact Image Sensor (CIS) as the imagesensor, whereas older drum scanners use a photomultiplier tube as the image sensor. A rotary scanner, usedfor high-speed document scanning, is another type of drum scanner, using a CCD array instead of aphotomultiplier
Other types of scanners are planetary scanners, which take photographs of books and documents, and 3Dscanners, for producing three-dimensional models of objects.Another category of scanner is digital camera scanners, which are based on the concept of reprographiccameras. Due to increasing resolution and new features such as anti-shake, digital cameras have become anattractive alternative to regular scanners. While still having disadvantages compared to traditional scanners(such as distortion, reflections, shadows, low contrast), digital cameras offer advantages such as speed,portability and gentle digitizing of thick documents without damaging the book spine. New scanningtechnologies are combining 3D scanners with digital cameras to create full-color, photo-realistic 3D modelsof objects.
Magnetic Ink Character Recognition, or MICR, is a character recognition technology used primarily by thebanking industry to facilitate the processing of cheques. The technology allows computers to readinformation (such as account numbers) off of printed documents. Unlike barcodes or similartechnologies, however, MICR codes can be easily read by humans.MICR characters are printed in special typefaces with a magnetic ink or toner, usually containing iron oxide.As a machine decodes the MICR text, it first magnetizes the characters in the plane of the paper. Then thecharacters are then passed over a MICR read head, a device similar to the playback head of a tape recorder.As each character passes over the head it produces a unique waveform that can be easily identified by thesystem.The use of magnetic printing allows the characters to be read reliably even if they have been overprinted orobscured by other marks, such as cancellation stamps. The error rate for the magnetic scanning of a typicalcheck is smaller than with optical character recognition systems. For well printed MICR documents, the"cant read" rate is usually less than 1% while the substitution rate (misread rate) is in the order of 1 per100,000 characters.
Optical character recognition, usually abbreviated to OCR, is the mechanical or electronic translation ofimages of handwritten, typewritten or printed text (usually captured by a scanner) into machine-editabletext. It is used to convert paper books and documents into electronic files, for instance, to computerize anold record-keeping system in an office, or to serve on a website such as Project Gutenberg. By replacing eachblock of pixels that resembles a particular character (such as a letter, digit or punctuation mark) or word withthat character or word, OCR makes it possible to edit printed text, search it for a given word or phrase, storeit more compactly, display or print a copy free of scanning artifacts, and apply such techniques as machinetranslation, text-to-speech and text mining to it. OCR is a field of research in pattern recognition, artificialintelligence and computer vision. Though academic research in the field continues, the focus on OCR hasshifted to implementation of proven techniques. Optical character recognition (using optical techniques suchas mirrors and lenses) and digital character recognition (using scanners and computer algorithms) wereoriginally considered separate fields. Because very few applications survive that use true opticaltechniques, the OCR term has now been broadened to include digital image processing as well.
The Optical Mark Reader is a device the "reads" pencil marks on NCS compatible scan forms such as surveysor test answer forms. If that all seems overly technical to you, just think of it as the machine that checksmultiple choice computer forms. In this document The Optical Mark Reader will be referred to as thescanner or OMR. The computer test forms designed for the OMR are known as NCS compatible scan forms.Tests and surveys completed on these forms are read in by the scanner, checked, and the results are saved toa file. This data file can be converted into an output file of several different formats, depending on whichtype of output you desire.The OMR is a powerful tool that has many features. If you are using casstat (grading tests), the OMR willprint the number of correct answers and the percentage of correct answers at the bottom of each test. Itwill also record statistical data about each question. This data is recorded in the output file created when theforms are scanned
A graphics tablet (or digitizing tablet, graphics pad, drawing tablet) is a computer input device that allowsone to hand-draw images and graphics, similar to the way one draws images with a pencil and paper. Thesetablets may also be used to capture data or handwritten signatures.A graphics tablet (also called pen pad or digitizer) consists of a flat surface upon which the user may "draw"an image using an attached stylus, a pen-like drawing apparatus. The image generally does not appear on thetablet itself but, rather, is displayed on the computer monitor. Some tablets however, come as a functioningsecondary computer screen that you can interact with directly using the stylus.Some tablets are intended as a general replacement for a mouse as the primary pointing and navigationdevice for desktop computers.
A touch screen is a computer display screen that is also an input device. The screens are sensitive topressure; a user interacts with the computer by touching pictures or words on the screen. There are threetypes of touch screen technology:Resistive: A resistive touch screen panel is coated with a thin metallic electrically conductive and resistivelayer that causes a change in the electrical current which is registered as a touch event and sent to thecontroller for processing. Resistive touch screen panels are generally more affordable but offer only 75%clarity and the layer can be damaged by sharp objects. Resistive touch screen panels are not affected byoutside elements such as dust or water.
Surface wave: Surface wave technology uses ultrasonic waves that pass over the touch screenpanel. When the panel is touched, a portion of the wave is absorbed. This change in theultrasonic waves registers the position of the touch event and sends this information to thecontroller for processing. Surface wave touch screen panels are the most advanced of the threetypes, but they can be damaged by outside elements.Capacitive: A capacitive touch screen panel is coated with a material that stores electricalcharges. When the panel is touched, a small amount of charge is drawn to the point of contact.Circuits located at each corner of the panel measure the charge and send the information to thecontroller for processing. Capacitive touch screen panels must be touched with a finger unlikeresistive and surface wave panels that can use fingers and stylus. Capacitive touch screens arenot affected by outside elements and have high clarity
The processed input data into a useful form is called output when input data is processed, computergenerates several types of output, depending upon the hardware and software used and the requirementsof the user. The user use output on a screen, prints it on the printer or hear it through speakers or head sets.Therefore, output is normally classifieds as:Softcopy Output The output received on the display screen or in the audio or video form is called softcopyoutput. This kind of output is not tangible and can not the touched. The most popular and commonly usedsoftcopy output device is display screen . Hardcopy Output The output printed on the paper is called hardcopy. The printers and plotters devices areused for this purpose. Sound Output The output received into the form of sound is called sound output. The speakers are mostcommonly used to receive the sound output.An output device is a hardware component used to get output from the computer. A number of outputdevices are available. The commonly used output devices include display device (Monitor), printer, speakerand headset, fax machine etc.
A monitor or display (sometimes called a visual display unit) is an electronic visual display for computers.The monitor comprises the display device, circuitry, and an enclosure. The display device in modernmonitors is typically a thin film transistor liquid crystal display (TFT-LCD), while older monitors use a cathoderay tube (CRT).The size of a display is usually given as the distance between two opposite screen corners. One problem withthis method is that it does not distinguish between the aspect ratios of monitors with identical diagonalsizes, despite the fact that the area of a given diagonal span decreases as it becomes less square. Forexample, a 4:3 21-inch (53.3 cm) monitor has an area of about 211 sq in (1,361 cm2), while a 16:9 21-inchwidescreen has about 188 sq in (1,213 cm2).This method of measurement is from the first types of CRT television, when round picture tubes were incommon use. Being circular, they only needed to use their diameter to describe their tube size. When roundtubes were used to display rectangular images, the diagonal measurement was equivalent to the roundtubes diameter. This method continued even when cathode ray tubes were manufactured as roundedrectangles.
1. The Enhanced Graphics Adapter (EGA) : is the IBM PC computer display standard specification located between CGA and VGA in terms of color and space resolution. Introduced in 1984 by IBM for its new PC- AT, EGA produces a display of 16 simultaneous colors from a palette of 64 at a resolution of up to 640×350 pixels. The EGA card includes a 16 kilobyte ROM to extend the system BIOS for additional graphics functions and includes the Motorola MC6845 video address generator as used in the CGA.Each of the 16 colors can be assigned a unique RGB color code via a palette mechanism in the 640×350 high- resolution mode; the 64 palette colors are a balanced RGB color set comprising all possible combinations of two bits per pixel for red, green and blue. EGA also includes full 16-color versions of the CGA 640×200 and 320×200 graphics modes2. VGA is referred to as an "array" instead of an "adapter" because it was implemented from the start as a single chip (an ASIC), replacing the Motorola 6845 and dozens of discrete logic chips that covered the full-length ISA boards of the MDA, CGA, and EGA. Its single-chip implementation also allowed the VGA to be placed directly on a PCs motherboard with a minimum of difficulty (it only required video memory, timing crystals and an external RAMDAC), and the first IBM PS/2 models were equipped with VGA on the motherboard. (Contrast this with all of the "family one" IBM PC desktop models—the PC [machine-type 5150], PC/XT , and PC AT —which required a display adapter installed in a slot in order to connect a monitor.)
A computer printer is a computer peripheral device that produces a hard copy (permanent human-readabletext and/or graphics usually on paper) from data stored in a computer connected to it. A virtual printer is apiece of computer software whose user interface and API resemble that of a printer driver, but which is notconnected with a physical computer printer.INKJET PRINTERAn inkjet printer is a type of computer printer that reproduces a digital image by propelling variably-sizeddroplets of liquid material (ink) onto a page. Inkjet printers are the most common type of printer and rangefrom small inexpensive consumer models to very large and expensive professional machines.BARCODE PRINTERA barcode printer (or bar code printer) is a computer peripheral for printing barcode labels or tags that canbe attached to physical objects. Barcode printers are commonly used to label cartons before shipment, or tolabel retail items with UPCs or EANs.The most common barcode printers employ one of two different printing technologies. Direct thermalprinters use a printhead to generate heat that causes a chemical reaction in specially designed paper thatturns the paper black. Thermal transfer printers also use heat, but instead of reacting the paper, the heatmelts a waxy or resin substance on a ribbon that runs over the label or tag material . The heat transfersink from the ribbon to the paper. Direct thermal printers are generally less expensive, but they producelabels that can become illegible if exposed to heat, direct sunlight, or chemical vapors.Barcode printers are designed for different markets. Industrial barcode printers are used in large warehousesand manufacturing facilities. They have large paper capacities, operate faster and have a longer service life.
CHARACTER MATRIX PRINTERCharacter matrix printers are a category of computer printers (typically impact printers) thatplace characters from a fixed character set anywhere onto a fixed grid of possible locations onthe page. Examples of these are daisy wheel printers, golf ball printers, chain printers, and bandprinters. A character printer prints one character at a time.DOT MATRIX PRINTERA dot matrix printer or impact matrix printer is a type of computer printer with a print headthat runs back and forth, or in an up and down motion, on the page and prints by impact,striking an ink-soaked cloth ribbon against the paper, much like the print mechanism on atypewriter. However, unlike a typewriter or daisy wheel printer, letters are drawn out of a dotmatrix, and thus, varied fonts and arbitrary graphics can be produced. Because the printinginvolves mechanical pressure, these printers can create carbon copies and carbonless copies.LETTER QUALITY PRINTERA letter-quality printer operates in much the same fashion as a typewriter. An array of letters,numbers, or symbols embossed on a metal surface, are used to strike a ribbon of ink, depositingthe ink on the page and thus printing a character.LASER PRINTERA laser printer is a common type of computer printer that rapidly produces high quality text andgraphics on plain paper. As with digital photocopiers and multifunction printers (MFPs), laserprinters employ a xerographic printing process but differ from analog photocopiers in that theimage is produced by the direct scanning of a laser beam across the printers photoreceptor.
THERMAL PRINTERA thermal printer (or direct thermal printer) produces a printed image by selectively heatingcoated thermochromic paper, or thermal paper as it is commonly known, when the paperpasses over the thermal print head. The coating turns black in the areas where it is heated,producing an image. Two-color direct thermal printers are capable of printing both black and anadditional color (often red), by applying heat at two different temperatures.Thermal transfer printing is a related method that uses a heat-sensitive ribbon instead of heat-sensitive paper
PlotterA plotter is a computer printing device for printing vector graphics. In the past, plotters were widely used inapplications such as computer-aided design, though they have generally been replaced with wide-formatconventional printers, and it is now commonplace to refer to such wide-format printers as "plotters," eventhough they technically arent.Drum PlotterA drum plotter is also known as Roller Plotter. It consists of a drum or roller on which a paper is placed andthe drum rotates back and forth to produce the graph on the paper. It also consists of mechanical deviceknown as Robotic Drawing Arm that holds a set of colored ink pens or pencils. The Robotic Drawing Armmoves side to side as the paper are rolled back and forth through the roller. In this way, a perfect graph ormap is created on the paper. This work is done under the control of computer. Drum Plotters are used toproduce continuous output, such as plotting earthquake activity.Flatbed PlotterA flatbed plotter is also known as Table Plotter. It plots on paper that is spread and fixed over a rectangularflatbed table. The flatbed plotter uses two robotic drawing arms, each of which holds a set of colored inkpens or pencils. The drawing arms move over the stationary paper and draw the graph on the paper.Typically, the plot size is equal to the area of a bed. The plot size may be 20- by-50 feet. It is used in thedesign of cars, ships, aircrafts, buildings, highways etc. Flatbed plotter is very slow in drawing or printinggraphs. The large and complicated drawing can take several hours to print. The main reason of the slowprinting is due to the movement mechanical devices.Today, mechanical plotters have been replaced by thermal, electrostatic and ink jet plotters. These systemsare faster and cheaper. They also produce large size drawings.
Micrographic plotterThese plotters don’t use drums. The paper or any other medium is held on both sides at the edges bypinch wheels which give back and forth movement of paper.Inkjet plotterThese plotters use inkjets in place of ink pens. The paper is placed on a drum and inkjets with differentcolored inks are mounted on a carriage. These are capable of producing multicoloured large drawings.
A computer has a very large memory. It can store a vast amount of information and can recall thatinformation instantly and correctly whenever desired. Human beings can do it only to a certain extent.Whenever a human being acquires new knowledge, the brain subconsciously retains what it feels isimportant. This is not the case with a computer. It has a large internal memory. Its memory can store allthe contents of your syllabus and can reproduce them fully or in parts as and when desired by you.Primary MemoryPrimary memory is one of the most important part of the computer, as it determines size and the number ofprogramsthat can be simultaneously held within the computer and as well as the amount of data that can beprocessed quickly.Primary memory stores necessary programs of system software, which are required to execute userprograms. The main memory is directly addressed by the CPU.The main memory can be divided into two parts: .1. RAM (Random-Access Memory)2. ROM (Read-Only Memory)Random-Access Memory (RAM)
Random access memoryRandom-access memory (usually known by its acronym, RAM) is a form of computer data storage. Today, ittakes the form of integrated circuits that allow stored data to be accessed in any order (i.e., at random). Theword random thus refers to the fact that any piece of data can be returned in a constant time, regardless ofits physical location and whether or not it is related to the previous piece of data. By contrast, storage devices such as magnetic discs and optical discs rely on the physical movement of therecording medium or a reading head. In these devices, the movement takes longer than data transfer, andthe retrieval time varies based on the physical location of the next item.The word RAM is often associated with volatile types of memory (such as DRAM memory modules), wherethe information is lost after the power is switched off. Many other types of memory are RAM, too, includingmost types of ROM and a type of flash memory called NOR-Flash. Software can "partition" a portion of acomputers RAM, allowing it to act as a much faster hard drive that is called a RAM disk. Unless the memoryused is non-volatile, a RAM disk loses the stored data when the computer is shut down. However, volatilememory can retain its data when the computer is shut down if it has a separate power source, usually abattery.Read only memoryRead-only memory (usually known by its acronym, ROM) is a class of storage media used in computers andother electronic devices. Because data stored in ROM cannot be modified (at least not very quickly oreasily), it is mainly used to distribute firmware (software that is very closely tied to specific hardware, andunlikely to require frequent updates)In its strictest sense, ROM refers only to mask ROM (the oldest type of solid state ROM), which is fabricatedwith the desired data permanently stored in it, and thus can never be modified. However, more moderntypes such as EPROM and flash EEPROM can be erased and re-programmed multiple times; they are stilldescribed as "read-only memory"(ROM) because the reprogramming process is generallyinfrequent, comparatively slow, and often does not permit random access writes to individual memorylocations.
Representing Characters in MemoryInformation in a computer is stored in the form of strings of Os and 1s. The symbols 0 and 1, known asbinary digits, are called bits. The memory of a computer can be thought of as cells. Each of these cellscontains one bit of information, i.e., each cell will have its state as 0 or 1.The combination of 8 bits form one byte. Each byte represents one character such as A, B, etc.Combination of bits is also used to store instructions and data in the computer memory. A nibble is acombination of 4 bits. It can store one decimal digit in its binary form.A group of bits representing data or instruction that forms the basic information unit of the computer iscalled a word. A word may be of 8, 16, 32, 48 bits or more. The size of the word depends on the architectureof the computer. A word can also be defined in terms of bytes. Since each byte is a combination of 8 bits, aword of 16-bit size can be called a 2-byte word. Each word of information is retrieved or stored as a unit incomputer Thus a machine with 16-bit words will be slower than a machine with 32-bit words.Most microprocessor based computers have 16-bit or 32-bit words.One byte is the smallest unit which can represent a data item or a character. Other units of memory areKB, MB, GB, TB.One Kilobyte (KB) means 210 bytes, i.e., 1024 bytes.One Megabyte (MB) means 210 KB, i.e., 1024 x 1024 bytes.One Gigabyte (GB) means 210 MB, i.e., 1024 x 1024 x 1024 bytes.One Terabyte (TB) means 210 GB, i.e., 1024 x 1024 x 1024·x 1024 bytes.
Secondary MemorySince a computers main memory is temporary, the secondary memory is used for bulk storage of programs,data, and other information. It has a much larger capacity than the main memory. The secondary memory isnon-volatile. The two most common secondary storage devices are the floppy disk and the hard disk.Hard DiskThe hard disk is made up of a collection of disks known as platters . These platters are coated with a materialthat allows data to be magnetically recorded. The disks rotate at a very high speed. A typical speed is 3600revolutions per minute. The read/write head moves across the disk surface. Hard disks can store more datathan floppy disks. Hard disk of size 40 GB is available. They are installed inside the computer and can accessthe data more quickly than floppy disks.Floppy DisksFloppy disks are individually packed disks. The recording medium on floppies is a myler or vinyl plasticmaterial with magnetic coating on one or both sides. These plastic disks, coated with magnetic material, arepermanently sealed in a square plastic jacket to protect them from dust and scratches. An elongated slot iscut in the jacket to enable read/write head access information from anywhere in this slot.Magnetic TapesMagnetic tapes are similar to audio or video tapes except for the difference that magnetic tapes are withmagnetizable material. A large variety of magnetic tapes are available commercially. The older type waswith 1 inch width and 1200 feet length and one foot diameter. Currently smaller size tapes, calledcartridges, are available that are of the size of audio and video cassettes.
CD-ROM (Compact Disc-Read-Only Memory)The CD-ROM stands for Compact Disc-Read-Only Me CD-ROMs are used to distribute a wide variety ofinform from multimedia encyclopedias to books, to games, to image video libraries, to product and salespresentations, and The advantage is that it is a portable media and can con ..large amount of data.To read a CD-ROM a device called CD-ROM drive is needed . Any information or data on CD-ROM can beerased or written onto with the help of a special device called CD recorder.CD-ROM are available in two forms:CD-R It is also called as the recordable-CD. It is written once and can be read again and again. Data oncewritten cannotbe erased.CD-RW It is also called as erasable-CD. It is a recording system that allows the user to erase previouslyrecordedinformation and then to record new information onto the same physical location on the disk.DVD (Digital Versatile Discs)DVD The next generation of CD-ROMs is called DVD-ROM that stands for Digital Versatile Disk. A DVD is thesame size asa Compact Disc but holds up to 25 times more matter and is much faster. This increased capacity allows DVDto storehigh-quality video as well as higher-than-CD-quality audio. The most notable advantage of DVD is itscapacity.This allows the ability to access much more data than standard CD-ROM for computer application.
Physically, a CD-ROM and a DVD-ROM disk are similar.DVD represents the first merging of three technologies, namely computer, audio, and television, into onecommon format.Cache MemoryA cache memory is a hardware system used for swapping of information between primary and secondarystorage devices. Generally, data is transferred from the main memory to ALU in computer words, one wordat a time. In cache memory many words from primary memory are transferred to temporary storage areacalled cache while CPU is busy in processing the information from the main storage. Now, if informationplaced in cache is required by ALU, it can be transferred to it easily. Cache memory is much faster.