MATHS FACTS AND FORMULA
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IMPORTANT SYMBOLS AND TABLES
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WHAT IS COMPUTER
INTRODUCTION TO COMPUTERS
DEVELOPMENT OF A COMPUTER PROGRAM
INPUT OUTPUT DEVICES1
BASICS OF COMPUTERS
NETWORK PROTOCOL BASICS
NETWORKED AROUND US
HOW TO SHARE A NET CONNECTION
SETTING UP YOUR NETWORK
ADVANCED HOME NETWORKING
NETWORKING AND BEYOND
MEDIA ACCESS METHODS
VIRTUAL PRIVATE NETWORK
STORAGE AREA NETWORK
TYPES OF PRINTER
INPUT OUTPUT DEVICES
MS SHORTCUT KEYS
MAC OS X LION: FINDER KEYBOARD SHORTCUTS
KEBOARD SHORTCUTS FOR MS Office 2007
MAC OS X KEYBOARD SHORTCUTS
MEMORY OF THE COMPUTER
MOST POPULAR SOCIAL NETWORKING SITES
MOST POPULAR SEARCH ENGINES
SHORTCUT KEYS FOR MS OUTLOOK
SHORTCUT KEYS FOR MS POWER POINT
SHORTCUT KEYS FOR MS EXCEL
POPULAR SEARCH ENGINES
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QUANTITY AND UNIT
FACTS ABOUT YOUR BODY
STD IX AND X
BEING ALIVE–WHAT DOES IT MEAN
CELL AS A UNIT OF LIFE
CELLULAR MACRO MOLECULES
NATURAL RESOURCES AND THEIR UTILISATION
NATURE AND SCOPE OF BIOLOGY
ORGANISMS AND THEIR ENVIRONMENT
SOME FUNGAL DISEASES
WILDLIFE AND FOREST CONSERVATION
SKELETON SYSTEM - Q & A
MINERALS AND THEIR SIGNIFICANCE TO A HUMAN BODY
FACTS ABOUT OUR BODY
SOME BIOLOGY FACTS
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RELATIVE ATOMIC MASSES
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STATES OR PHASES OF MATTER
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SCIENTIFIC INSTRUMENTS AND WHAT THEY MEASURE
CONFUSING WORDS AND THEIR MEANINGS
PROVERB WITH B
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INSTRUMENTS AND WHAT THEY MEASURE
LIST OF PREPOSITION
LIST OF VERBS
LIST OF COMMON PRONOUNS
ONE WORD SUBSTITUTION
AIR AROUND US
CHANGES AROUND US
COMPONENTS OF FOOD
FIBER AND FABRICS
GETTING TO KNOW PLANTS
STORING MATERIALS INTO GROUPS
GARBAGE IN GARBAGE OUT
THE LIVING ORGANISMS AND THEIR SURROUNDINGS
MOTION AND MEASUREMENT OF DISTANCES
LIGHT, SHADOWS AND REFLECTIONS
ELECTRICITY AND CIRCUITS
SEPARATION OF SUBSTANCES
NUTRITIONS OF PLANTS
NUTRITION IN ANIMALS
FIBRE TO FABRIC
PHYSICAL AND CHEMICAL CHANGES
COAL AND PETROLEUM
WEATHER, CLIMATE AND ADAPTATIONS OF ANIMALS
WIND STORM AND CYCLONES
CROP PRODUCTION AND MANAGEMENT
MICROORGANISMS: FRIEND AND FOE
SYNTHETIC FIBERS AND PLASTICS
MATERIALS: METALS AND NON-METALS
COAL AND PETROLEUM I
COMBUSTION AND FLAME
CONSERVATION OF PLANTS AND ANIMALS
CELL - STRUCTURE AND FUNCTIONS
REPRODUCTION IN ANIMALS
REACHING THE AGE OF ADOLESCENCE
JUNIOR SCIENCE DICTIONARY
ANNIVERSARIES AND DAYS
IMPORTANT DATES IN INDIAN HISTORY
ANNIVERSARIES AND DAYS I
IMPORTANT INDIAN BATTLES
IMPORTANT SESSIONS OF CONGRESS
OLYMPIC GAMES DETAIL
TOP MEDAL WINNERS
FIRST IN INDIA
NATIONAL ANIMALS AND BIRDS
LONGEST HIGHEST LARGEST
FACTS ABOUT EARTH
SOUNDS MADE BY SOME OBJECTS
MCQ ON IMAGINARY LINES
MULTIPLE CHOICE QUESTIONS
MCQ ON IMAGINARY LINES - SET 2
HERITAGE SITES OF INDIA
STATES OF INDIA
LIST OF COUNTRIES AND THEIR CAPITALS
COUNTRY SPECIFIC DOMAINS
COUNTRIES OF ASIA
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INTERNATIONAL COUNTRY CALLING CODE
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COLOUR TERMS I
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DISTRICTS IN INDIA
VEDIC / MENTAL MATHEMATICS
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SQUARING A 2 DIGIT NUMBER
DOUBLE AND HALF METHOD
SQUARING A NUMBER ENDING IN 5
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SQUARING A NUMBER ENDING IN 7
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PHYSICAL GEOGRAPHY OF INDIA
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INPUT OUTPUT DEVICES1
INPUT – OUTPUT DEVICES
After completing this unit, you will be able to:
· Understand the various Input Devices.
· Understand the various Output Devices.
· Understand how Storage Devices work.
· Understand the working of Communication Devices.
3.2 Input Devices
3.3 Output Devices
3.4 Communication Devices
3.5 Storage Devices
3.7 Self-Assessment Questions
Input devices are devices that bring information into a computer. Pure input devices include punched card readers, paper tape readers, keyboards, mouse, drawing tablets, touchpads, trackballs, game controllers, etc.
Output devices are devices that are responsible for retrieving information. Pure Output devices include cardpunches, paper tape punches, LED displays (for light emitting diodes), monitors, printers, pen plotters, etc. Output devices can be classified as softcopies and hardcopies. Softcopy comprises of all the varied types of monitors where the user can see only the information displayed/retrieved based on certain processing instructions whereas the hardcopy comprises of all the varied types of printers wherein the user can print the information on paper.
3.2 INPUT DEVICES
1. The Keyboard - Standard Keyboard Layout
A standard computer keyboard has about 104 keys. Most keyboards use the QWERTY layout, named for the first six keys in the top row of alphabets.
Fig 3.1: Keyboard
A keyboard can be divided into five groups of keys which are:
· Alphanumeric keys.
· Numeric keypad.
· Function keys.
· Modifier keys.
· Cursor movement keys.
include all the alphabets usually required for typing from A-Z, 0-9 along with the special character keys viz. !@#$%A&*Q~ etc.
is separately placed on the right side of the keyboard which includes all the numeric keys viz. 0-9 along with the most frequently used mathematical operators viz. +-*/. As it is a group it becomes easy for the operators to feed in the numeric data easily and faster.
are placed as the first row in a keyboard labeled from F1 to F12 and each of these keys are assigned a specific function. These keys are used as a shortcut key to perform certain tasks. The functionality of the keys differs from software to software and these keys are also programmable. For example, FI is usually reserved for Help.
are Ctrl and Alt. When used in combination with some other key, they have been programmed to perform certain tasks. The functionality of the combination keys are programmable and can differ from software to software. For example, Alt + F4 is a combination of keys to close any Window program. Ctrl + C is used to copy selected text in most of the application software(s) available.
keys are the keys that help the user or the operator to navigate in a text or any document. These keys are placed in between the alphanumeric keyset and the numeric keypad. These include Page Up, Page Down, Home, End, Delete, Insert, Left, Right, Up and Down.
When you press a key, the keyboard controller detects the keystroke. The controller places a scan code in the keyboard buffer, indicating which key was pressed .The keyboard sends the computer an interrupt request, telling the CPU to accept the keystroke.
Fig 3.2 Internet Working of a Keyboard
The mouse is also referred as a pointing device. It is used to move a graphical pointer on the screen to point to any location on the screen.
Fig 3.3: Mouse
The mouse can be used to issue commands, draw and perform other types of input tasks. Normally a mouse is used for performing the following operations such as Select, Click, Double Click, Drag and Drop.
A mouse is used to point to any location on the screen by moving the on-screen pointer to the desired location. Simply click the left mouse button once.
A mouse usually has 2 buttons or 3 buttons with the scroll in the middle of both the buttons. Usually most of us use the left mouse button to perform a select operation. A right click is often used to invoke a shortcut menu.
Usually when we refer to a double click, it is a left mouse button and it involves clicking the left mouse button twice in quick succession. This operation leads to opening the selected application or file.
Drag and Drop:
Hold down the left mouse button as you move the pointer and release the button; the selected item will be placed there.
Fig 3.4: Light Pen
A light pen is a pointing device. It is used to select a displayed menu option on the Monitor (CRT). It is a photosensitive pen-like device. It is capable of sensing a position on the screen when its tip touches the screen. When its tip is moved over the screen surface, its photocell-sensing element detects the light coming from the screen and the corresponding signals are sent to the processor. As the menu is a set of programmed choices offered to the user, it automatically positions the cursor on the screen. The user indicates his choice by touching the light pen against a desired description of the menu. The signals sent by the light pen to the processor identify the menu option.
Fig 3.5: Joystick
A joystick is also a pointing device. It is used to move the cursor position on a CRT screen. Its function is similar to that of a mouse. A joystick is a stick which has a spherical ball at its lower end as well as at its upper end. The lower spherical ball moves in a socket. The joystick can be moved right or left, forward or backward. The electronic circuitry inside the joystick detects and measures the displacement of the joystick from its central position. This information is sent to the processor.
Fig 3.6: Trackball
A trackball is like a mouse turned upside-down. Users use their thumb to move the exposed ball, and their fingers to press the buttons to perform click actions. The movement of the ball is sent to the processor which detects the, signals and positions the cursor on the screen
6. Track pads
Fig 3.7: Trackpad
A track pad is a touch-sensitive pad that provides the same functionality as a mouse. To use a track pad, you, glide your finger across its surface. Track pads provide a set of buttons that function like mouse buttons.
Scanners are a type of input devices which are widely used for graphical input. They are capable of entering information directly into the computer. The main advantage of a direct entry of information is that users do not have to key in the information, which automatically reduces the degree of errors. This provides faster and more accurate data entry. Scanners popularly used are Optical Scanners and Magnetic-Ink Character Readers.
Fig 3.8: Scanner
The optical scanners are capable of reading information recorded on paper and employing light source and light sensors. The information to be scanned may be typewritten information or information coded as ink or pencil marks or bars. The following are the commonly used optical scanners:
Optical Character Readers (OCR):
An optical character reader detects alphanumeric characters printed or typewritten on paper. The text which is to be scanned, is illuminated by a low-frequency light source.
The light is absorbed by the dark areas and reflected from the lighted areas. The reflected light is received by photocells or CCDs (charged coupled devices) which provide binary data corresponding to dark and lighted areas. An OCR can scan several thousands of printed or typewritten characters per second. Optical character readers are used in large-volume applications such as computer-oriented bills prepared by public utilities.
Optical Mark Readers (OMR):
Special marks such as squares or bubbles are prepared on examination answer sheets or questionnaires. The users fill in these squares with soft pencil or ink to indicate their choice. These marks are detected by an optical mark reader and the corresponding signals are sent to the processor. If a mark is present, it reduces the amount of reflected light. If a mark is not present, the amount of reflected light is not reduced. This change in the amount of reflected light is used to detect the presence of a mark. This method is used where one out of a few numbers of alternatives is to be selected and marked. For example, market surveys, population surveys, objective type answer sheets, etc. where choice is restricted to one out of a few choices.
Optical Bar Code Readers:
This method uses a number of bars (lines) of varying thickness and spacing between them to indicate the desired information. Bar codes are used on most grocery items. An optical bar reader can read such bars and convert them into electrical pulses to be processed by a computer. The most commonly used bar code is Universal Product Code (UPC). The UPC code uses a series of vertical bars of varying widths. These bars are detected as ten digits. The first five digits identify the supplier or manufacturer of the item. The second five digits identify the product. The code also contains a check digit to ensure that the information read is correct.
Magnetic Ink Character Readers (MICR): MICR is widely used by banks in advanced countries to process large volumes of cheques and deposit forms written by customers every day. A special ink called magnetic ink (an ink which contains iron oxide particles) is used to write characters on cheques and deposit forms which are to be processed by an MICR. MICR is capable of reading characters written with magnetic ink on a paper. The magnetic ink is magnetized during the input process. The MICR reads the magnetic patterns of the written characters. To identify the characters, these patterns are compared with special patterns stored in the memory. When a cheque is entered into an MICR, it passes through a magnetic field. The iron oxide particles are magnetized under the magnetic field. The read head reads the characters written with magnetic ink on the cheque. It interprets the characters and sends the corresponding data directly to the computer for processing.
8. Video Input Devices
A digital camera is an electronic device to transform images into electronic data. Modern digital cameras are typically multifunctional and the same device can take photographs, video, and also offers sound.
Video cameras such as those used in television and movie production typically have multiple image sensors (one per color) to enhance resolution and color gamut. Professional video cameras usually do not have a built-in VCR or microphone.
Fig 3.9: Digital Camera
are usually used by amateurs. These are a combination of a camera and a VCR to create an all-in-one production unit. They generally include a microphone to record sound, and feature a small LCD to watch the video during filming and playback.
are digital cameras attached to computers and used for video conferencing or other purposes. Webcams can capture full-motion video as well, and some models include microphones or zoom ability. Many digital cameras can connect directly to a computer to transfer data. Early cameras used the PC serial port. USB is the most widely used method, though some have a Fire Wire port or use Bluetooth. Some cameras such as the Kodak EasyShare One are able to connect to computer networks wirelessly via Wi-Fi. Some devices, like mobile phones and PDAs, contain integrated digital cameras. Mobile phone cameras are even more common than stand-alone digital cameras. Digital cameras need memory to store data.
3.3 OUTPUT DEVICES
1. Video Display Units
The output devices receive information from the computer and provide them to users. The output devices commonly used with general purpose computers are:
CRT Screen Terminals.
CRT Screen Terminals.
A CRT terminal consists of a CRT display unit, a keyboard, CRT refresh RAM, and CRT controller for communications with the computer. Modem CRT terminals contain one or more built-in microprocessors to control and coordinate keyboard, CRT display unit and data transmission from the terminal to the computer and vice-versa. The data is entered into the computer through the keyboard. Each entered character is also displayed on the CRT screen, so that the user can see what he has typed. When data is keyed in, it is held in a small memory called a buffer, within the terminal itself. The data is not transmitted to the computer until the user presses an enter key on the keyboard. A small square pointer on the screen, called a cursor indicates the spot on the screen where the next character to be keyed in will be displayed. To correct keystroke errors, the cursor is moved to the position where the correction is to be made. Then the key for the correct character is pressed. Since the terminals are used for interaction with operators, fast data transmission is not required. Therefore, usually data is transmitted from the terminal to the computer and vice -versa in a serial mode i.e. one bit at a time.
A character is displayed on the screen by light dots. A matrix of dots is used for this purpose. To display a character the size of the dot-matrix may be 5.7, 7.9 or 7.12. The desired dots are lighted to display a character. A ROM called character generator ROM, stores the dot patterns for the display of each character. The ASCII or EBCDIC codes of characters of a text to be displayed at a time on the screen, are stored in a RAM, called display RAM or video RAM or display refresh RAM. When new text is to be displayed, the contents of the RAM are changed accordingly. A CRT screen displays 25 lines (rows), each line (row) containing 80 characters.
A modem CRT display has considerable flexibility: it can often handle a range of resolutions from 640 by 480 pixels (640x480) up to 2048 by 1536 pixels (2048x 1536), with 32-bit colour and a variety of refresh rates. Dot pitch measures the sharpness of a display. In general, the lower the dot pitch, (such as.24), the sharper the picture will appear. Early CRT-based VDUs (Visual Display Units) without graphics capabilities gained the label “glass teletypes”, because of the functional similarity to their electromechanical predecessors. Black-and-white displays can only display one colour: either as on or off. Monochrome displays can show only levels of a single colour. In both cases the display usually uses green, orange (amber) or gray (white).
Non-CRT displays include LED, LCD and plasma displays. LED displays are used in microprocessor-based industrial controls, instruments, etc. where only a small amount of data is to be displayed. CRT screen display is used where a large amount of data is to be displayed. In portable battery powered instruments, LCD displays are usually used because they consume less power. Non-CRT displays have been described below in brief.
Liquid Crystal Displays (LCDs)
In LCDs a liquid crystalline material is placed between two glass or plastic plates. The front plate is transparent and the back plate is reflective. There is a coating of thin film on the front plate. The coating is transparent and conductive. Its sections (segments) are in the shape of desired characters. Commonly available LCDs are of two types:
dynamic scattering type
field effect type
. LCDs do not emit their own light. Therefore, a light source is to be used. LCDs simply change the reflection of available light. Today, most LCDs used are of the type that produces dark images on a silver background.
In plasma displays, ionized gas is placed between two glass plates. A number of parallel wires run horizontally as well as vertically. A small amount of current is passed through one horizontal and one vertical wire to cause the gas to glow at a spot at the intersection of the wires. The IBM 581 display employs 960 horizontal and 768 vertical pixels as compared to IBM-PC colours graphics adapter which is provided with 320 by 200 pixels in medium resolution, and 640x200 in high resolution. The plasma display screens are costly. These are available only on selected models of portable computers.
Printers are the most popular output devices. They provide information in a permanent readable form. They produce printed outputs of results, programs and data.
A classification of printers on the basis of how they print is given here:
: A character printer prints one character of the text at a time.
A line printer prints one line of the text at a time.
A page printer prints one page of the text at a time.
A classification of printers on the basis of the technology used in their manufacturing process is given here:
Impact printers use an electro-mechanical mechanism that causes hammers or pins to strike against a ribbon and paper to print the text. Impact printers can produce multiple copies of the text. Printing is slow as compared to non-impact printers.
: Non-impact printers do not use any electro-mechanical printing head to strike against ribbon and paper. They use thermal, chemical, electrostatic, laser beam or inkjet technology for printing the text. Printing is faster as compared to impact printer. Non-impact printers can produce only a single copy of the text.
Types of Impact Printers:
Dot Matrix Impact Type Character Printer
Fig 3.10: Dot Matrix Printer
A character is printed by printing the selected number of dots from a matrix of dots. Figure. 3.10 shows a dot matrix printer. Figure 2.14 shows the print head mechanism of a dot matrix printer. Figure 2.15 shows the printed character. The print head contains a vertical array of 7, 9, 14, 18 or even 24 pins. A character is printed in a number of steps. One dot-column of the dot matrix is taken up at a time. The selected dots of a column (the column of dot-matrix) are printed by the print head as it moves across a line.
The line printer prints one line of the text at a time. Its printing speed lies in the range of 300-3000 lines per minute. It is used for large-volume printing jobs. It may be used with both mini and mainframe computers.
A drum printer uses a rapidly rotating drum (cylinder) which contains a complete set of raised characters in each band around the cylinder. Each character position along the text line contains a band of raised character set. There is a magnetically driven hammer in each character position of the line. The printer receives all characters to be printed in one line of the text from the processor. The hammers hit the ribbon and paper against the desired character on the drum when it comes in the printing position. Its noise level is high. Its speed varies from 200 to 2000 lines per minute.
Types of Non-Impact Printers:
Fig 3.11: Laser Printer
They print one page at a time. These printers use laser or some other light source to produce an image on a photosensitive drum. The computer controls the laser beam to turn it on and off when it is sent back and forth across the drum. An image is produced following the raster scan principle. The laser-exposed areas attract toner (an ink powder). Thereafter the drum transfers the toner to the paper. The paper then moves to a fusing station where the toner is permanently fused on the paper with heat or pressure. After this the drum is discharged and cleaned. Now the drum is ready for processing the next page. The laser printers are quiet and they produce high-quality output. These printers are expensive and require periodic maintenance. Low-speed laser printers produce 10 pages or more per minute and are used with microcomputers. High-speed laser printers producing up to 300 pages per minute are used with mini and large computers. Laser printers have become popular for voluminous printing work. They are used for desk top publishing work also.
Fig 3.12: Plotter
A plotter is a vector graphics printing device that connects to a computer. Plotters print their output by moving a pen across the surface of a piece of paper. This means that plotters are restricted to line art, rather than raster graphics as with other printers. They can draw complex line art, including text, but do so very slowly because of the mechanical movement of the pens. (Plotters are incapable of creating a solid region of colour; but can hatch an area by drawing a number of close, regular lines.) Another difference between plotters and printers is that a printer is aimed primarily at printing text. This makes it fairly easy to control, simply sending the text to the printer is usually enough to generate a page of output. This is not the case of the plotter, where a number of printer control languages were created to send the more detailed information like “draw a line from here to here”.
2. Computer Speakers
Fig 3.13: Computer Speakers
The external speakers and are usually equipped with a male-end phone plug for computer sound cards; however, there are some that have female RCA (phono) plug ports, and some people link computer sound cards to nearby stereo systems. Computer speakers are usually a simplified stereo system without a radio or other media sources built in. Typically, the simplest computer speakers come with computers. There are advanced forms of computer speakers that have graphic equalization features (bass, treble, etc.) for dynamic audio flexibility. The base of a Harman / kardon speaker. Computer speakers range from a twin set of simple speakers to 5.1 surround sound speakers with advanced features. The high-end surround sound speakers give the best sound for computer gaming but are rather expensive.
3.4 COMMUNICATION DEVICES
These are peripheral equipment that allows data from one computer to be transferred to another computer. Communication devices allow computers to “talk” to one another.
These include the following:
b. Network Cards (Ethernet cards)
c. Serial Ports
d. Parallel Ports
e. SCSI Ports
The modem is a device that allows a computer to be connected to your telephone line. Modems may be installed inside the computer's case or connected to the computer's exterior serial port. Once connected, you can send or receive faxes and electronic mail. Many people are purchasing modems today so they can connect their computers to the Internet. The Internet is a vast connection of about 100 million computers worldwide. It provides instantaneous access to thousands of companies, news services, libraries and individuals anywhere in the world. Today, the industry standard modem transmits data at 57,000 bits per second or bps (NOT bytes per second). They are often called 56K modems. These models are less expensive models and can transmit data at 28,800 bps.
Input/Output (I/O) ports are used to connect external devices such as a printer to the computer. Standard computer system I/O includes one parallel port, two serial ports, one game port end one PS/2 type port.
The parallel port is used to connect a local printer. The first parallel port is assigned the name LPT1. The 9 pin serial port is used to connect a serial mouse. This port can be assigned the name COM1, COM2, COM3, or COM4. COM1 is typical. A second 25 pin serial port is available for additional serial devices. An external MODEM connects to a serial port. It can be assigned the name COM1, COM2, COM3, or COM4. It just can't use the same name as any other serial port in your system. COM2 is a typical parallel port used for the printer, external ZIP drives, scanners and cameras. These use a 25-pin connector on the PC.
It is used for external modems, mice and connecting instruments. Most new ports use a 9-pin connector, but some older ones have a 25-pin connector.
(Universal Serial Bus) a faster and better connection that lets you change components on the fly. The computer should recognize the peripheral and not require re-booting. The connectors are small rectangular plugs.
(Small Computer System Interface) less common standard for computers that requires interface cards that look like large printer connectors.
3.5 STORAGE DEVICES
Floppy Disk Drive
A floppy disk drive is a removable storage device that reads and writes information magnetically on floppy disks. Diskettes provide another option for secondary storage that allows users to carry their files with them. The hard drive is mounted inside the system unit and only removed when upgrading or repairing the system. A floppy provides removable storage.
The drawback to a diskette is the capacity. A 3.5 inch high density diskette holds 1.44 MB of information. This is plenty of space for word documents and text, but if your file contains pictures, a floppy's capacity will most likely be inadequate. The name ‘floppy’ refers to the thin, plastic, flexible disk inside the hard plastic cover that magnetically records information.
· Consists of magnetic "platter" that rotates at the speed of approximately 360 rpm.
· Read and Write heads are in close contact with the surface of the disk or plate.
· Usually very low capacity storage (usually around 1.44 MB).
Hard Disk Drive
The hard disk drive is the main secondary storage device used to provide the ability to permanently store information. When you are working in a program, such as MS Word, the document you are creating is stored temporarily in the computer's memory (RAM). If you want to store the document for future use, you need to save it to a secondary storage media. A good choice is the computer's hard drive. If you do not save the document, once the document is closed or the computer is turned off, the document will be lost forever. Another important function of a hard disk drive is to store program files. When you purchase a new program, you need to install the program files to your hard drive before you can use the program. Most programs will not work unless they have been properly installed to a hard disk drive. Personal computers have at least one hard disk drive installed inside the system unit. If more storage capacity is required, additional hard drives can be installed.
Secondary storage devices are called read/write devices because data can be written (saved) and can be read (retrieved) from them for the life of the media.
Data is stored magnetically on disks in bytes. The
of a hard disk drive is a measure of how much information it can store and is measured in bytes. A 2GB hard disk drive can store close to 2,147,483,648 characters. This is approximately equal to two thousand novels. This sounds large, but for today's robust applications like Windows 95, 2 GB can quickly be used up by the applications installed leaving very little storage space for data and documents created by the user. Programs installed and stored on a hard disk drive, depending on the complexity of the application, may require several hundred megabytes of storage space each. Purchase the largest hard disk drive you can afford.
The way a computer uses memory and how it uses storage is important to understand. Memory called RAM, only stores data and programs that are being processed. Secondary storage devices store data and programs that are not being processed. This difference is important to understand because it could mean losing hours of hard work by forgetting to save your file. A hard disk drive can be thought of as a file cabinet. To work on a file, you need to retrieve it from the file cabinet and place it on your desk; the desk is the computer's memory (RAM).
This is why people often say, “If it is running, it is in the RAM.” The stored data is transferred from the hard drive to the systems memory. The only way the edited file can get back from the desk into the file cabinet with the new changes is to save it. Computers can only process what has been transferred from storage devices or input from an input device to the main memory in the system. The internal hard drive is connected to a disk controller with a cable. The most popular type of connection is IDE (Integrated Drive Electronics) because it is the least expensive and reliable. Other connection types used are Enhanced IDE (EIDE) and Small Computer System Interface (SCSI), pronounced “scuzzy."
· Consists of magnetic “platter” that rotates at speeds of 3600+ rpm.
· Read and Write heads ‘floats’ over the surface of these platters.
· Usually high capacity storage (range from 40MB to I0GB+).
Hard disks can be of two types:
1. Fixed: what we think of as hard drives inside the computer box.
2. Removable: disk cartridges such as Zip or Jazz disks.
(Zip disks: Stores 100 - 250 MB and JAZZ disks: Stores I or 2 GB).
The key difference between floppy disks and hard disks is that the floppy disk’s head is in close contact with surface of the disk whereas in the case of hard disks the heads “fly” on a film of air, a fraction of a mm above the disk's surface. If the head touches dirt or the disk then you have what is called a “head crash” which destroys the surface of the disk and the disk head.
A CD ROM drive is a removable storage device that reads information stored on a compact disk. Compact disks are optical storage media which are read with laser light. CD ROM drives can be mounted inside the computer case or connected externally by a cable. A CD ROM disk can store 650 mega bytes of data which is much greater than a normal diskette.
The drawback is that most of the CD ROM drives are only readable and not writable though writable media is available for that use.
CD ROM drives are useful for installing programs and for running applications that install some of the files to the hard drive and execute the program by transferring the data from the CD ROM to the memory while the program is running.
The most important specification for a CD ROM drive is its speed. The speed of a CD ROM drive determines how fast a disk will spin. The faster the disk spins, the faster data can be transferred from the disk to the computer's memory. This results in better performance. A CD ROMs speed is indicated by a number followed by an X. For example, a twelve-speed CD ROM drive is a 12x. The larger the number, the faster the CD ROM drive can spin the CD ROM disk. Two other specifications are usually considered when rating a CD ROM drive; the
data transfer rate
Access time is how quickly the data you are looking for can be located on the disc and data transfer rate is how fast the data can be transferred from the disc to the computer's memory. CD ROM drives can be purchased as IDE or SCSI type drives. SCSI CD ROM drives require an additional adapter board installed in the system to control them.
CD-ROMs store 650 MB, or 74 minutes of CD quality music (so about 9 MB/minute).
CD-Rs (CD-Recordable) can be "burned" once. The media cost is negligible.
CD-RWs (CD-Rewrite) can be written over.
OTHER STORAGE MEDIA
This type combines the features of magnetic and optical technology. The magnetic field effect actually changes the polarity of the spot while recording. Usually it has a capacity ranging from 500 megabytes to 2.3 giga byte.
These are very small m size and most often used with the portable computers and can store more than 300 mega bytes of data.
Credit card-sized devices that contain a microprocessor in the center left section. Microprocessors can store up to 8,000 bytes of information. Examples of these cards include prepaid telephone cards and employee time and attendance tracking cards.
Storage devices in which data is placed and/orretrieved by means of a focused optical beam; for example, optical tape storage, optical disk storage, optical card storage. Optical techniques may also be combined with other techniques such as in magneto-optical storage. These are also called WORM Drives, Optical Disk Libraries, Jukeboxes, Write-Once-Read-Many Devices, Optical Storage, Optical Jukeboxes, Write-Once-Read-Many Drives, and WORM Devices.
Input devices are devices that bring information into a computer. Pure input devices include punched card readers, paper tape readers, keyboards, mouse, drawing tablets, touchpad’s, trackballs, game controllers, etc.
Output devices are devices that are responsible for retrieving information. Pure output devices include cardpunches, paper tape punches, LED displays (for light emitting diodes), monitors, printers, pen plotters, etc.
Communication devices are responsible for establishing communication channels between two PCs or an ISP, if required. Some of the communication devices and components include modems, network cards (Ethernet cards), serial ports, parallel ports, SCSI ports, etc.
Some of the storage devices are:
Magnetic storage devices: Floppy disks, hard disk and magnetic tapes.
Optical storage devices: CD ROM, DVD.
Optical-magnetic device: WORM Drives, Optical disks, jukeboxes.
These storage devices may be accompanied by the basic system and may also vary based on user requirements.
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