PC Computer Hardware Output Devices Pt 1

PC Computer Hardware Output Devices

Visual Display Unit (VDU) The Screen or Monitor

Till third generation of computer it was not possible to verify whether the program being typed into computer‘s memory is correct or correctly entered. It was possible only when microcomputer was introduced. The micro computer consisting of one visual display unit as essential part on which the user can directly see, whatever he or she typing on keyboard. When key is pressed corresponding character is displayed on VDU. The result of the calculation or manipulation can also be seen directly on visual display unit and that to instantaneously. By addition of this unit you can be interactive with computer, i.e. Can talk to comport by typing query and computer will answer your query.
Visual display unit looks likes a color television and is fabricated as integral part of microcomputer. Sometimes it may be an independent unit and connected to keyboard and CPU by flexible chords. Quite often the VDU houses the floppy disk drive. The home computer can be attched to color television itself but thruogh a interfacing device. Some television have this interfacing device in built with them

VDUs screen is made up Cathode Ray Tube (CRT) due to which it is also called CRT terminal. When the data input is fed through the key board of the computer, electrical signals are generated; the CPU converts these signals into alphanumeric or graphic display. So the output is obtained as optical display. It contains about 20 to 40 rows of horizontal lines with each lines divided into 80 space. Some computers are provided with the facility of changing the modes of operation. In that case the number of columns and rows will change. The mode of dividing the screen to the several small squire grid areas for visual display is known as resolutions. One squire area is meant for displaying one dot. A group of several dots makes up a pixel. Every character is made up for several pixels. When the entire screen is divided into high number of squire areas , then that particular mode are VDU is said have high resolution. With high resolution screen the information more accurately represented.

The screen is coated with dots for phosphors called pixel from inside. The more is number of pixels from inside. The more is number of pixels or dots. In a screen, the better will be capability of computer to display the information. The phosphors can be made to glow red, green or blue by firing electons at them from behind.

The electrons have to be guided to the right spot through the vertical and horizontal deflection systems. This is ensures that the beam lights up the right phosphors to produce the correct image on the screen.

All the times , the screen deals with tiny points of light, grouped together , form letters or numbers . It is moves so fast that you never notice all the steps involved inputting together a screen full of information. To make it even faster, microcomputers often have ROM (Read Only Memory) the monitors can be broadly classified as :

MONOCHROME MONITORS

COLORED MONITORS

MONOCHROME MONITOR

These are generally black and white monitors or green phosphor monitors they do not receive TV signals.

COLOR MONITORS

The colors are the human perception of the different wavelengths of light. It is possible

to create almost all visible colors using two systems of primary colors. On a color monitors, colors are displayed as varying intensities of red, green and blue dots. When red, green and blue are turned on high, white is produced. As the intensities are equally lowered, shades of grey are produced. When all dots are turned off, the base color of the screen appears.

LIQUID CRYSTAL DISPLAY (LCD)

In LCD’s liquid crystalline material is sandwiched between glass or plastic plates. The front plate is transparent and the back plate is reflective. There is a coating a of thin film on the front plate. The coating transparent and conductive. It is selection (segments) are in the shape of desired characters LCD’s don not emit their own light therefore, a light source is to be used. LCD’s simply changed the reflection of available light.

LCD TECHNOLOGY

A liquid crystal display is a thin, light weight display device with no moving parts. It consists of eclectically – controlled light- polarizing liquid trapped in cells between two transparent polarizing sheets. Polarizing axes of the two sheets are aligned in the same direction. Each cell is supplied with electrical contacts that allow an electric field to be applied to the liquid. Before an electric field is applied, the molecules in the liquid are in a relaxed state. Light can pass through the liquid without any effect o its direction of polarization , so entire assembly appears transparent . When an electric field is applied, the molecules in the liquid twist in to an excited state, causing the axis of polarization of the light to rotate. Thus the light has been polarized by passing through the first sheet , then rotated by passing trough the liquid , now has the wrong polarization of penetrate the second sheet . The result is that the activated part of the display appears dark .

TRANSMISSIVE AND REFLECTIVE DISPLAYS

LCD can be used in transmissive and reflective modes. A transmissive LCD is illuminated from one side and viewed from the opposite side. An activated cell therefore appears dark while inactive cells appear bright. This type is high brightness application such pocket television receivers. The lamp is used to illuminate the LCD in such product usually consumes more battery power that the LCD itself.

A reflective LCDs, are used in pocket calculators and digital watches, is viewed by ambient light reflected in a mirror behind the display. This type has lower contrast than the transmissive type, because the ambient light passes twice trough the display before reaching the viewer. The advantage of this type is that no lamp to consume power, so the battery life is long. A small LCD consumes so little power that can run a photovoltaic cell.

COLOR DISPLAYS

The liquid crystal used in LCD rotates all visible wavelength equally, but additional refinements have been added to the basic LCD to produce a color display.

In a color LCD each pixel is divided into three sections, one with red filter, one with green filter and one with blue filter the pixel can be made to appear an arbitrary color by varying the relative brightness of its three colored sections.

THIN FILM TRANSISTOR DISPLAY

An LCD is made with either a passive matrix display grid. The active matrix LCD is known as TFT (thin film transistors) display. The passive matrix has a grid of conductors with pixels located at each intersection in the grid a current is end across two conductors on the grid to control the light of any pixel. An active matrix has transistor located at each pixel intersection, requiring less current to control the luminance of a pixel. For this reason the current is on active matrix display can be switched on and off more frequently, improving the screen refresh time.

Medium sized displays, such as those in monochrome personal organizers and pocket television set, have a passive matrix structure. This type has one set of contacts for each row and column of the display, rather than one for each pixel. However the disadvantage is that only one pixel can be address at any instant. The other pixels have to remember their last state until the control circuit has time to revisit them. This results in reduced contrast and poor response to fast moving images. As the number of pixels increases, this type of displays becomes less and less attractive.

For high resolution color displays such as large LCD monitors, an active matrix system is used. The LCD panel contains, besides the polarizing sheets and cells of liquid crystal, a matrix of transistors. These devices store the electrical state of each pixel on the display while all the other pixel are being updated. This method provides much better brighter, sharper displays.

PC Computer Hardware Input Devices Part 2

DIGITIZER

A digitizer is an input device that converts graphic and pictorial data to digital (binary) form which can be direct fed and stored inside a computer. There are two types of digitizers: rectangular- coordinate or flatbed digitizer and image- scan digitizer. In case of a flatbed digitizer, the drawing to be digitized is spread and fixed over a rectangular flatbed table. A mechanism is now moved over the surface of the drawing that scan the drawing and produces signals related to X and Y coordinates of the table. Image scan digitizers scan and reproduce entire drawing and photographs automatically. They are costlier and more powerful than the flatbed digitizers and are capable of digitizing not only the shape and size of the drawing but also the varying intensities on a gray to black scale at different points of the drawing. Thus, flatbed digitizers are mainly use to digitize simple drawing, graphs, charts, etc. and image- scan digitizers are used to digitize more complex pictures and photographs.

VOICE RECOGNITION SYSTEM

This is an input device; consist of a microphone or telephone that converts human speech into electrical signals. A signal pattern obtained in this manner is transmitted to the computer where it is matched against pre stored patterns to identify the input. When a close match is found, a word is recognized by the system. T he set of pre stored patterns is known as the vocabulary of the system. T o build up this vocabulary, the system has to be trained to recognize the words and phrases that are to present in the vocabulary. Hence the system is initially operated in a “training mode “when the user speaks the words and phases (to be sorted in the vocabulary) several times to train the system to recognize his / her particular voice pattern. In this mode, the patterns are created and stored for future matching. Because the accent of different speakers varies, most recognize system, are speaker dependent. How ever, a system may be trained to recognize the voice of more than one operator in which case a different vocabulary is maintained for each operator. These systems are used where a person wants to input data to a computerized system in situations where his hands are busy, or his eyes must be fixed on a measuring instrument or some other object.

OPTICAL MARKS READER (OMR)

It is a device for checking the documents and question papers. Now a days it is quite a common practice to the knowledge and IQ level of candidate by multiple choice objective type questions. The candidates are required write there answer by putting a standard dot in front of the correct answer with help of specially designed soft pencils. While evaluating the answer paper , OMR directs a thin beam of light is transmitted through the dot as compared to nearby surface due to which answer is recognized by the computer.. The OMR can evaluate only those documents which are printed with marked positions in the specified areas. OMR can read about 10,000 document per hour, and thus can print the result within the same day without any favoritism or mistake.

OPTICAL CHARACTER READER (OCR)

This is also a device for reading the documents. It can read alphanumeric characters created in a particulars style or good quality paper using special ink. The shape of character is recognized by OCR with help of light source in conjunction with photo electric cells. Optical characters are being extensively used for billing purposes, i.e. preparation of electricity bills and insurance premium renewals.

BAR CODE READERS

This method uses a number of bars (lines) of varying thickness and spacing between them to indicate the desired information. Bar code reader can read such bars and converts them into electrical pulses to be processed by a computer. The most common used bar code is Universal Product Code (UPC). The UPC code uses a series of vertical bars of varying width. These bars are detected as ten digits. The first five digits identify the supplier or manufacturer of item. The second five digits identify individual product code. The code also contains a check digit to ensure that the information read is correct or not.

MAGNETIC INK CHARACTER READER (MICR)

It uses a special ink that can be magnetized so that the individual characters can be recognized by the reader from the shape of the wave form of the electrical pulses induced in the magnetism. Such a system uses special inks containing magnetic particles of iron oxide. The characters are printed in a very distinctive style. When such documents are passed through a strong magnetic field, the ink coded characters become magnetized. MICRs have got reading speed about 24000 documents per minute. Such a character recognition system is now being used by all commercial banks even in India a MICR coded cheque.

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PC Computer Hardware Input Devices Part 1

PC COMPUTER HARDWARE

INPUT DEVICES

Data and instruction must enter the computer system before any computation can be performed on the supplied data. This task is performed by the input unit that links the external environment with the computer system. An input device converts input data and instruction into suitable binary form which can be accepted by computer. The commonly used input device is keyboard. A number of input devices are there which do not required typing for inputting information e. i. mouse, light pen, joy stick track ball, touch screen etc. However regardless of their inputs all input devices must provide a computer with data that are transformed into the binary code that the primary memory of computer is designed to accept. This transformation is done by unit called input interfaces..

In short, the following functions are performed by input unit

• It accepts [or reads] the list of instructions and data from the outside world.
• It converts these instruction and data in computer acceptable form (electronic pulses).
• It supplies the converted instructions and data to the computer system for further processing
  

The input unit may be any one or combination of two or mare units out of following.

• Punched card
• Punched Paper Tape
• Keyboard
• Light pen
• Mouse
• Joy Stick
• Digitizer
• Voice recognition System
• Optical marker reader
• Optical Character reader
• Magnetic ink Character Recognition System

PUNCHED CARDS

This was earliest method of feeding data into computer. First punched card system was introduced by Dr. Hermann Hollerith in year 1887 for US census. The most popular design of punched chard was introduced by computer company IBM. The punch card is little longer and less broader than Indian Post Card, It contains total eighty column and twelve rows. Each column is meant for punching a pattern of square type holes for each character. The punching is done with the help of card punching machine which is very similar to a typewriter. When you press a key marked A, the card puncher will punch two holes as per code.

PUNCHED PAPER TAPE

A strip of paper 12.5 mm to 75mm wide and 90 to 300 m long was used for feeding data into computers in previous years.

The data is punched on these tapes with the help of a tape puncher using eight channel code or five channel 29 code . Corresponding to each character, a pattern of circular hole is generated according to certain code.


KEYBOARD

Each micro computer consists of a key board as input unit . In addition, the key board contains several command keys and function keys. Beneath each key . There is set of electrical contacts, which are closed when the key is pressed. By closing the electronic circuit, a signal (corresponding to character contained by key) is produced which is sensed by computer. This signal makes the character pressed to appear on the screen. Multi lingual key boards have been also devised.

Keyboards of special design are used for musical computer. In such key, piano type keys are provided through which any tune can be played . The standard IBM PC keyboard can be divided into three general areas:

• Typewriter area , having the standard set of alphabet letters and number keys.
• Function keys F1 through F12- which have different functions depending on the software in use. F1 is mostly used for getting help

Numeric keypad, having cursor control and number keys. Some on this pad have dual roles and the required number is obtained by either pressing along with shift key or by first pressing NUMLOCK key . The number keypad is used for entering large amount of numeric data.

GRAPHIC INPUT

Any information in the form drawing can be put into computer’s memory on visual display unit. The graphic pad has a magnetically sensitive surface that allows shapes to be drawn with the help of an electronic pen. The movement of pen is sensed by the electronic circuit below the pad which converts the movement signals into binary electrical pulses. These pulses travel into CPU of computer that displays the information on screen of VDU.


LIGHT PEN

Light pen is a device which enables us to write anything directly on the screen of computer. We can draw sketches and diagrams also. The light pen has got a tip which is very much sensitive to light. Actually it is a photosensitive detector. A bright spot of light known as raster spot moves in a orderly way across the back of computer‘s screen which alerts the tip of light pen.

MOUSE

A mouse is also a pointing device. It is held in one hand and moved across a flat surface. About the size of the normal cake of bath soap, it usually rolls on a small rubber ball and has two or three buttons on the top. When the user rolls the mouse across the flat surface the cursor on the screen moves in the direction of mouse movement, giving the user a sense of pointing at something on screen.

Positioning a cursor with a mouse is easier for non typists than pressing various key combinations. With proper software, a mouse can also be used to draw pictures on screen and edit text , as is done with software like Ventura, CorelDraw, etc. in DTP system.


JOYSTICK

A joystick is also used to move the cursor position on screen its function is similar to that of a mouse. Children can play with computers in a simple way by the use of joystick. While paying video games like SPACE- INVANDERS, user need to move space craft quickly across the screen. This can be done by pressing key on keyboard but it is neither convenient nor comfortable for small children to use the key board . This type of action can be better done with the help of joystick. As move the stick around in its socket the movements are translated into binary instructions with the help of electrical contacts.

More

Part

PC Computer Hardware Overview

A DESCRIPTIVE OVERVIEW OF PC COMPUTER HARDWARE

Is general term used to represent the physical and tangible component of the computer i.e. those component which can be seen and touched . It includes:

1. Input Unit
2. output Unit
3. Central processing unit
4. Backing storage and auxiliary memory devices.

The electronic circuits consisting of resistors, capacitors, ICs main computer equipment( visually the keyboard, visual display unit and central processing unit) and its peripherals like floppy drives, joystick, printer, tracker ball ,graphic pad, plotters, digitizer, card reader, paper and magnetic tapes and disks, modems, interfaces terminals etc. are all examples of computer hardware . All input and output devices connected to computer are collectively known as peripherals.

INPUT UNIT

Input unit is actually a device which provides man to machine communication with computer. Input of any form is first converted into binary electronic signals which can be understood by CPU. This process is called digitizing.

Input may be linguistic, graphical, mechanical, audio, visual or audiovisual .Linguistic input is written program in computer’s programming languages which is inputted to computer either by typing on keyboard, or by floppy, magnetic tapes or CD, DVDs.

OUTPUT UNIT

Output unit works just in reverse manner of input units. We feed data into computer by typing on to the keyboard of computer. Similarly, information coming out of computer can be typed on the sheet of paper by an output unit known as printer, in a similar manner, as it happens is happens in teleprinters. Output coming from the CPU is in the form of electronic binary signals that needs conversion in a form, that can be easily understood by human being, i.e. graphical alphanumeric, audiovisual or in the form of human language. This function is performed by output units include, VDU, Plotter, printers, speech synthesizers, decoders, robots etc.

CENTRAL PROCESSING UNIT

CPU is totally electronic based and its function are to:

• Receive and store data into main storage memory.
• Control sequence of operations.
• Give command to all parts of the computer system.
• Carry out data processing and output the result.

The CPU assumes many different sizes in different computers. The CPU of mainframe computers are like large cup board and carry out millions of instructions in seconds The CPU of a microcomputer is much less powerful and is contained in a single chip.

This is actually the brain and heart of a computer. Data is processed here . It takes information from the input unit and process it accordingly to instructions . The instruction are given by programs. programs are written in languages which a computer can under stand. These are actually coded languages.

By data processing we means

• Making arithmetic calculation like addition , subtraction, multification, division and exponentiation etc.
• Making logical decision like comparing two values to find out which one geater.
• Manipulating alphanumeric

ARITHMETIC AND LOGIC UNIT (ALU)

The ALU is a section where all the arithmetic and logical functions are carried out. We know that every arithmetic operation required twooperands. The operation then process a result. This ALU, therefore, must be able to handle two data words and the result. This concept is dependent on the storage and processing techniques, which may vary , from model to model. Logical operation usually involve comparisons. Circuits an the ALU compare two values by subtracting one from another. For example, to determine whether number A is greater than number B , B is subtracted fro A and the sign of the result is determined . Depending on the sign of the result , the ALU does further operation. Alphabetic data also compared according to their assigned order sequence.
ALU comprises a number of accumulators and registers. It derives all the data from the main memory as directed by control unit based on program given to it. This data gets loaded into accumulators in ALU. For example , if numbers A and B are to be added the control unit selects number A from its address in memory and loads it into arithmetic unit, Then the value of B is selected and added to A in the arithmetic unit. The results are placed in the main storage(again under the direction of control unit ) or may be retained in the accumulators themselves for further calculation. Some logical operation of the ALU enable the computer to have the decision making quality.

CONTROL UNIT

The control unit direct all the operation inside the computer. It is known as nerve centre of the computer, because it controls and coordinates all hardware operation, i.e, those of the CPU and input-output devices. It performs following actions
It gives command to transfer data from input device to memory of arithmetic and logic unit. It also transfer result from ALU to memory and on to the output device for printing.
It stores the program in the memory, takes instruction one by one , understand them and issue appropriate commands to other units.
It fetches the required instructions from the main memory storage via memory data register(MDR) and places it in the control instruction register (CIR). Then it interprets the instruction in CIR and gets it executed by sending a command signal to the concerned hardware device. Memory data register is a special register which holds all data instructions temporarily, as they pass in and out of the main memory, Control instruction register is also a special register which holds machine instructions currently being interpreted by control unit.

MEMORY

Digital computer use the binary number system, which has two digit : 0 and 1. A binary digit is called a bit . Information is represented in digital computer I n groups of bits.
The bit is an elementary of Memory.
A group of 8 bit is called a byte and a group of 4 bit is called nibble.

One byte is the smallest unit which represents data. Other bigger units of memory are KB , MB and GB which has following relation:
1KB=1024Byte(210 Byte)
1MB=1024KB=024x1024bytes
1GB=1024 MB =1024 x 1024 x1024 bytes.
Memory of storage devices are two types:

• Internal Primary . or Main Storage or Immediate Access Storage (IAS).
• Auxiliary memory storage or backing storage.

INTERNAL MEMORY OR IMMEDIATE ACCESS STORAGE (IAS)

It is also called computer ‘s main or primary memory because like human it is able to store information which can be recalled or accessed when required . The program of instruction s has to be stored in the main memory in order to make it work automatically. This memory forms an integral part of ALU and is synthesized wholly by electronic components due to which its operation is extremely fast.

Any item of data or any instruction stored in the memory can be retrieved (called back) by the computer at lightning speed. Modern computer does this in few nanoseconds. Only a limited storage is provided as it is very costly. The rest of the program and data are kept in secondary storage devices also known as backing storage devices.

Internal memory of a modern computer is contained in silicon chips which are of two types

Read only memory (ROM)
Random Access Memory (RAM)

RAM CHIPS

RAMs are designed to act as short term memory, and therefore also known as volatile memory. A RAM holds information which is needed for particular operation. New information can be recorded, read and then rubbed out when no longer needed. But once the computer switched off, a RAM forgets everything.

ROM CHIPS

ROMs are Read Only Memories holds sets of instruction which tell the microprocessor to do. For instance, a ROM will tell the computer, how to recognize keys and which key is to be pressed and how to light up the screen.
Information stored in ROM can only be read. It can not be rubbed out or added to. It is permanently built in computer at the time of its production and therefore also known as firmware. ROM also holds the permanent data like trigonometric functions several variations of ROM are available.

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