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Storage device is a device which stores the data. Data and instruction entered into a computer system thorough i/p system has to be stored inside the computer before actual procession starts. Then after procession again need to store output or result to at storage device. Types
  1. Primary Storage
  2. Secondary Storage
Primary Storage
    • Also known as main memory
    • RAM(Random access memory)
    • Volatile memory
    • Faster
    • Very expensive
    • Low storage capacity
Secondary Storage
    • Also known as auxiliary storage.
    • Hard Disk
    • Non-volatile
    • Slower
    • Cheaper
    • Very High Storage.
computer storage hierarchy
computer storage devices hierarchy

  Random Access Memory (RAM)
  • Primary storage of a computer is often referred to as RAM because of its random access capability
  • RAM chips are volatile memory
  • A computer’s motherboard is designed in a manner that the memory capacity can be enhanced by adding more memory chips
  • The additional RAM chips, which plug into special sockets on the motherboard, are known assingle-in-line memorymodules (SIMMs)
  Read Only Memory (ROM)
  • ROM a non-volatile memory chip
  • Data stored in a ROM can only be read and used –they cannot be changed
  • ROMs are mainly used to store programs and data, which do not change and are frequently used.
  • For example,system boot program
  PROM(Programmable Read only memory).
  • Embedded system.
  • Small chip on the circuit which is programmed
  • Eg.
    • Printer,
    • Bios chip
    • Microwave ,
    • washing machine
EPROM
  • Erasable programmable Read only memory
  • Once information is stored in a ROM or PROM chip it cannot be altered.
  • EPROM ever comes this problem.
  • As the name suggest chip can be reprogrammed to store new information.
  Cache Memory
  • It is commonly used for minimizing the memory-processor speed mismatch.
  • It is an extremely fast, small memory between CPU and main memory whose access time is closer to the processing speed of the CPU.
  • It is used to temporarily store very active data and instructions during processing.
  • Cache is pronounced as “cash”
  Limitations of Primary Storage
  1. Limited capacity because the cost per bit of storage is high
  2. Volatile -data stored in it is lost when the electric power is turned off or interrupted
 

Secondary Storage

  • Used in a computer system to overcome the limitations of primary storage
  • Has virtually unlimited capacity because the cost per bit of storage is very low
  • Has an operating speed far slower than that of the primary storage
  • Used to store large volumes of data on a permanent basis
  • Also known as auxiliary memory
computer secondary storage hierarchy

   Sequential-access Storage Devices
  • Arrival at the desired storage location may be preceded by sequencing through other locations
  • Data can only be retrieved in the same sequence in which it is stored
  • Access time varies according to the storage location of the information being accessed
  • Suitable for sequential processing applications where most, if not all, of the data records need to be processed one after another
  • Magnetic tape is a typical example of such a storage device
  Direct-access Storage Devices
  • Devices where any storage location may be selected and accessed at random
  • Permits access to individual information in a more direct or immediate manner
  • Approximately equal access time is required for accessing information from any storage location
  • Suitable for direct processing applications such as on-line ticket booking systems, on-line banking systems
  • Magnetic, optical, and magneto-optical disks are typical examples of such a storage device
  Magnetic Tape Basics
  • Commonly used sequential-access secondary storage device
  • Physically, the tape medium is a plastic ribbon, which is usually ½inch or ¼inch wide and 50 to 2400 feet long
  • Plastic ribbon is coated with a magnetizable recording material such as iron-oxide or chromium dioxide
  • Data are recorded on the tape in the form of tiny invisible magnetized and non-magnetized spots (representing 1s and 0s) on its coated surface
  • Tape ribbon is stored in reels or a small cartridge or cassette
  Magnetic Tape –Tape Drive
  • Used for writing/reading of data to/from a magnetic tape ribbon
  • Different for tape reels, cartridges, and cassettes
  • Has read/write heads for reading/writing of data on tape
  • A magnetic tape reel/cartridge/cassette has to be first loaded on a tape drive for reading/writing of data on it
  • When processing is complete, the tape is removed from the tape drive for off-line storage
Types of Magnetic Tape
  1. ½-inch tape reel
  2. ½-inch tape cartridge
  3. ¼-inch streamer tape
  4. 4-mm digital audio tape (DAT)
Advantages of Magnetic Tapes
  1. Storage capacity is virtually unlimited because as many tapes as required can be used for storing very large data sets
  2. Cost per bit of storage is very low for magnetic tapes.
  3. Tapes can be erased and reused many times
  4. Tape reels and cartridges are compact and light in weight
  5. Easy to handle and store.
  6. Very large amount of data can be stored in a small storage space
  7. Compact size and light weight
  8. Magnetic tape reels and cartridges are also easily portable from one place to another
  9. Often used for transferring data and programs from one computer to another that are not linked together
Limitations of Magnetic Tapes
  1. Due to their sequential access nature, they are not suitable for storage of those data that frequently require to be accessed randomly
  2. Must be stored in a dust-free environment because specks of dust can cause tape-reading errors
  3. Must be stored in an environment with properly controlled temperature and humidity levels
  4. Tape ribbon may get twisted due to warping, resulting in loss of stored data
  5. Should be properly labeled so that some useful data stored on a particular tape is not erased by mistake
  Magnetic Disk -Basics
  • Commonly used direct-access secondary storage device.
  • Physically, a magnetic disk is a thin, circular plate/platter made of metal or plastic that is usually coated on both sides with a magnetizablerecording material such as iron-oxide
  • Data are recorded on the disk in the form of tiny invisible magnetized and non-magnetized spots (representing 1s and 0s) on the coated surfaces of the disk
  • The disk is stored in a specially designed protective envelope or cartridge, or several of them are stacked together in a sealed, contamination-free container
computer storage hard disk internal structure
 
computer storage Mahnetic Disks
    Floppy Disks
  • Round, flat piece of flexible plastic disks coated with magnetic oxide
  • So called because they are made of flexible plastic plates which can bend
  • Also known as floppies or diskettes
  • Plastic disk is encased in a square plastic or vinyl jacket cover that gives handling protection to the disk surface
  • The two types of floppy disks in use today are:
  • 5¼-inch diskette, whose diameter is 5¼-inch. It is encased in a square, flexible vinyl jacket
  • 3½-inch diskette, whose diameter is 3½-inch. It is encased in a square, hard plastic jacket
  • Most popular and inexpensive secondary storage medium used in small computers
  Hard Disks
  • Round, flat piece of rigid metal (frequently aluminium) disks coated with magnetic oxide
  • Come in many sizes, ranging from 1 to 14-inch diameter.
  • Depending on how they are packaged, hard disks are of three types:
  • Zip/Bernoulli disks
  • Disk packs
  • Winchester disks
  • Primary on-line secondary storage device for most computer systems today
  o  Zip/Bernoulli Disks
      • Uses a single hard disk platter encased in a plastic cartridge
      • Disk drives may be portable or fixed type
      • Fixed type is part of the computer system, permanently connected to it
      • Portable type can be carried to a computer system, connected to it for the duration of use, and then can be disconnected and taken away when the work is done
      • Zip disks can be easily inserted/removed from a zip drive just as we insert/remove floppy disks in a floppy disk drive
              o  Disk Packs
      • Uses multiple (two or more) hard disk platters mounted on a single central shaft
      • Disk drives have a separate read/write head for each usable disk surface (the upper surface of the top-most disk and the lower surface of the bottom most disk is not used)
      • Disks are of removable/interchangeable type in the sense that they have to be mounted on the disk drive before they can be used, and can be removed and kept off-line when not in use
                o  Winchester Disks
      • Uses multiple (two or more) hard disk platters mounted on a single central shaft
      • Hard disk platters and the disk drive are sealed together in a contamination-free container and cannot be separated from each other
Advantages of Magnetic Disks
  1. More suitable than magnetic tapes for a wider range of applications because they support direct access of data
  2. Random access property enables them to be used simultaneously by multiple users as a shared device. A tape is not suitable for such type of usage due to its
  3. sequential-access property
  4. Suitable for both on-line and off-line storage of data
  5. Except for the fixed type Winchester disks, the storage capacity of other magnetic disks is virtually unlimited as many disks can be used for storing very large data sets
  6. Due to their low cost and high data recording densities, the cost per bit of storage is low for magnetic disks.
  7. An additional cost benefit is that magnetic disks can be erased and reused many times
  8. Floppy disks and zip disks are compact and light in weight. Hence they are easy to handle and store.
  9. Very large amount of data can be stored in a small storage space
  10. Due to their compact size and light weight, floppy disks and zip disks are also easily portable from one place to another
  11. They are often used for transferring data and programs from one computer to another, which are not linked together
  12. Any information desired from a disk storage can be accessed in a few  milliseconds because it is a direct access storage device
  13. Data transfer rate for a magnetic disk system is normally higher than a tape  system
  14. Magnetic disks are less vulnerable to data corruption due to careless handling or unfavorable temperature and humidity conditions than magnetic tapes
Limitations of Magnetic Disks
  1. Although used for both random processing and sequential processing of data, for applications of the latter type, it may be less efficient than magnetic tapes
  2. More difficult to maintain the security of information stored on shared, on-line secondary storage devices, as compared to magnetic tapes or other types of magnetic disks
  3. For Winchester disks, a disk crash or drive failure often results in loss of entire stored data. It is not easy to recover the lost data. Suitable backup procedures are suggested for data stored on Winchester disks
  4. Some types of magnetic disks, such as disk packs and Winchester disks, are not so easily portable like magnetic tapes
  5. On a cost-per-bit basis, the cost of magnetic disks is low, but the cost of magnetic tapes is even lower
  6. Must be stored in a dust-free environment
  7. Floppy disks, zip disks and disk packs should be labeled properly to prevent erasure of useful data by mistake
  Optical Disk –Basics
  • Consists of a circular disk, which is coated with a thin metal or some other material that is highly reflective
  • Laser beam technology is used for recording/reading of data on the disk
  • Also known as laser disk / optical laser disk, due to the use of laser beam technology
  • Proved to be a promising random access medium for high capacity secondary storage because it can store extremely large amounts of data in a limited space
  • Has one long spiral track, which starts at the outer edge and spirals inward to the center
  • Track is divided into equal size sectors

computer storage opticaldisk
     Optical Disk Drive
  • Uses laser beam technology for reading/writing of data
  • Has no mechanical read/write access arm
  • Uses a constant linear velocity (CLV) encoding scheme, in which the rotational speed of the disk varies inversely with the radius
Type:
1)CD Rom Drive
2)Combo DVD
3)DVD Drive
 
Advantages of Optical Disks
    1. The cost-per-bit of storage for optical disks is very low because of their low cost and enormous storage density.
    2. The use of a single spiral track makes optical disks an ideal storage medium for reading large blocks of sequential data, such as music.
    3. Optical disk drives do not have any mechanical read/write heads to rub against or crash into the disk surface.  This makes optical disks a more reliable storage medium than magnetic tapes or magnetic disks.
    4. Optical disks have a data storage life in excess of 30 years.
    5. This makes them a better storage medium for data archiving as compared to magnetic tapes or magnetic disks.
    6. As data once stored on an optical disk becomes permanent, danger of stored data getting inadvertently erased/overwritten is removed
    7. Due to their compact size and light weight, optical disks are easy to handle, store, and port from one place to another
    8. Music CDs can be played on a computer having a CD-ROM drive along with a sound board and speakers. This allows computer systems to be also used as music systems
Limitations of Optical Disks
    1. It is largely read-only (permanent) storage medium. Data once recorded, cannot be erased and hence the optical disks cannot be reused
    2. The data access speed for optical disks is slower than magnetic disks
    3. Optical disks require a complicated drive mechanism
 

Memory Storage Devices

1)Flash Drive (Pen Drive)
  • Relatively new secondary storage device based on flash memory, enabling easy transport of data from one computer to another
  • Compact device of the size of a pen, comes in various shapes and stylish designs and may have different added features
  • Plug-and-play device that simply plugs into a USB (Universal Serial Bus) port of a computer, treated as removable drive
  • Available storage capacities are 8MB, 16MB, 64MB, 128MB, 256MB, 512MB, 1GB, 2GB, 4GB, and 8GB
2)Memory Card (SD/MMC)
  • Similar to Flash Drive but in card shape
  • Plug-and-play device that simply plugs into a port of a computer, treated as removable drive
  • Useful in electronic devices like Camera, music player
  • Available storage capacities are 8MB, 16MB, 64MB, 128MB, 256MB, 512MB, 1GB, 2GB, 4GB, and 8GB
 

Storage Hierarchy

  • As a single type of storage is not superior in speed of access, capacity, and cost, most computer systems make use of a hierarchy of storage technologies as shown below.
computer storage hierarchy

Evolution of Computers

Charles Babbage is considered to be the father of modern digital computers
  • He designed “Difference Engine”in 1822
  • He designed a fullyautomatic analytical engine in 1842 for performing basic  arithmetic functions
  • His efforts established a number of principles that are fundamental to the design of any digital computer

Computer Generations


Computer Generations overview
  • Generation”in computer talk is a step in technology. It provides a framework  for the growth of computer industry
  • Originally it was used to distinguish between various hardware technologies, but now it has been extended to include both hardware and software
  • Till today, there are five computer generations
computer generations third generations descriptions
computer generations fourth generations descriptions
computer generations fifth generations descriptions
computer generations hardwares


       

What is Computer?

Computer is an electronic device which is used to store the data, as per given instructions it gives results quickly and accurately.
introduction to computers

Data : Data is a raw material of information. Information : Proper collection of the data is called information.

Characteristics of Computer

  • SPEED : In general, no human being can compete to solving the complex computation, faster than computer.
  • ACCURACY : Since Computer is programmed, so what ever input we give it gives result with accuratly.
  • STORAGE : Computer can store mass storage of data with appropriate formate.
  • DILIGENCE : Computer can work for hours without any break and creating error.
  • VERSATILITY : We can use computer to perform completely different type of work at the same time.
  • POWER OF REMEMBERING : It can remember data for us.
  • NO IQ : Computer does not work without instruction.
  • NO FEELING : Computer does not have emotions, knowledge, experience, feeling.

Computer and its components

Computer : Computer itself a combination of different type of separate electronic device. i.e. Computer only will be computer if it has INPUT DEVICE, PROCESS UNIT, and OUTPUT DEVICE.
  • Central Processing Unit (CPU) : It is heart and mind of the computer without this unit computer unable to process.
  • Keyboard : This is an input device which is used to input the data into the computer.
  • Mouse : This is also an input device which is used to input the data into the computer.
  • Monitor : This is an output device which is used to show the result of the instructions.
There are variety of monitor available in the market such as, CRT Monitor, LCD Monitor, Touch Screen Monitor, TFT Monitor etc.
  • Switched Mode Power Supply (SMPS) : This is and electronic device which is used to manage the power supply of computer.
  • Hard Disk (HDD) : This is used to store the data in massive amount. There are so many type of HDD available in the market, i.e. SATA, PATA, External HDD, Internal HDD.
  • Printer : This is an out put device which is used to show the result on the paper. There are plenty of printer available in the market like inkjet, Laser printer, dot matrix printer etc.
  • Universal Serial Bus (USB) : This is used to connect the external device to the computer.
  • Ethernet Cable : This is used to connect computer with other computer.
  • CD/DVD ROM : This is used to store the data.
  • Speaker : This is an output device which is used to listen voice, songs, etc.
  • Mike : This is an Input device which is used to record the sound .
  • Laptop : This is complete computer which can be carried anywhere any time.
  • Netbook : This is called mini laptop which is generally lighter and smaller than laptop.
  • Random Access Memory (RAM) : This is called primary memory. This is also called main memory of the computer. Whatever data is written in this memory, is lost after switching off the system.
  • Read Only Memory (ROM) : This is called primary memory. Data is written in this memory by the vendor of the computer permanently.
  • Pen Drive : This is very popular device now a days for carrying data on move.
  • Blue Ray Disk : This is same as CD/DVD but only different is it can store multi time of data from CD/DVD and faster than CD/DVD.
  • Scanner : This is an input device which is used to scan the document for the soft copy.
  • LCD : It is known as Liqued Crystal Display. It is an output device as monitor.
  • Motherboard : It is a combination of electronic circuits.
  • Sound Card : This is also a combination of electronic circuits which helps to give out put in the form of sound.
  • Graphics Card : This is also a combination of electronic circuits which helps to give output the data into the monitor.

Computer Software

Software is a logical programme to handle/solve the complex problem.
  • System Software : This is special type of software which is responsible for handle the whole computer system.
  • Application Software : This is special type of software which is used to solve a particular problem.
  • Embeded Software : This type of software embeded with hardware to do a specific type of job.
  • Proprietary Software : In general, this type of software require to purchase to use that particular software for the some time or single user as per conditioned by the vendor of that particular software.
Open Source Software : This type of software may be freely available and can not be use in commercially. We can modify, and use it under the same license. 

Computer Languages

  • Machine Level Language : This is low level programming language. Computer or any electronic device only understand this language. i.e. Binary number i.e 0 and 1.
  • Assembly Level Language : This is a low level programming language which is converted into executable machine code by a utility programmer referred to as an assembler.
  • High Level Language : High level language is a programming language which is easily understandable/readable by human.
  • Interpreter : This is a convertor which converts high level language programme to low level language programme line by line.
  • Compiler : This is also a convertor which converts whole high level language programme to low level language programme at a time.

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