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Secondary%20Storage%20Memory

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Title: Secondary%20Storage%20Memory


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Secondary StorageMemory
  • Rashedul Hasan

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  • Secondary Storage

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Necessity of Secondary Storage
  • Primary storage has the following limitations,
  • Limited Capacity the storage capacity of
    primary storage of todays computer is not
    sufficient to store large volume of data.
  • Volatile the data stored in it is lost when the
    power is turned off or interrupted.
  • In order to overcome the above mentioned
    limitations we need auxiliary memory.

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Secondary Storage
  • Secondary storage devices permanently store hold
    data and Information as well as programs.
  • It is non-volatile.
  • Generally has an operating speed far slower than
    that of Primary storage.

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Sequential access devices Magnetic Tape
Memory Card (SD/MMC)
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Storage
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Magnetic Tape
  • Magnetic tape is a one-half inch or one-quarter
    inch ribbon of plastic material on which data is
    recorded. The tape drive is an input/output
    device that reads, writes and erases data on
    tapes. Magnetic tapes are erasable, reusable and
    durable. They are made to store large quantities
    of data inexpensively and therefore are often
    used for backup. Magnetic tape is not suitable
    for data files that are revised or updated often
    because it stores data sequentially.

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Magnetic Disk.
  • Magnetic disks are the most widely used storage
    medium for computers. A magnetic disk offers high
    storage capacity, reliability, and the capacity
    to directly access stored data. Magnetic disks
    hold more data in a small place and attain faster
    data access speeds. Types of magnetic disks
    mainly include, floppy disk and hard disks.

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Floppy Disk
  • The Floppy was introduced in the early 1970s by
    IBM as a new type of secondary storage.
    Originally they were eight inches in diameter and
    were thin and flexible which gave them the name
    floppy disks, or floppies. It was used as the
    principle medium of secondary storage for
    personal computers. They are available in two
    different sizes 3 1/2 inch and 5 1/4 inch.

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Hard Disks
  • Hard disks provide larger and faster secondary
    storage capabilities than diskettes. Usually hard
    disks are permanently mounted inside the
    computer. Most personal computers have at least
    one hard disk. The input/output device that
    transfers data to and from the hard disk is the
    hard disk drive.

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A Western Digital 3.5 inch 250 GB SATA HDD.
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A hard disk drive with the metal cover removed
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Hard Disk
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Hard Disk
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Sector, Track R/W Head
  • Tracks Data are recorded in concentric circles
    called Track.
  • Sectors Sections used for storage reference
    purpose.
  • Read/Write Head is used to transfer between the
    computer and the Disk.

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Close-up of a hard disk head
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An IBM HDD head resting on a disk platter.
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Characteristics
  • Data transfer rate As of 2008, a typical 7200
    rpm desktop hard drive has a data transfer rate
    of about 70 megabytes per second. This rate
    depends on the track location, so it will be
    highest for data on the outer tracks (where there
    are more data sectors) and lower toward the inner
    tracks (where there are fewer data sectors) and
    is generally somewhat higher for 10,000rpm
    drives. A current widely-used standard for the
    data transfer rate is 3.0 Gbit/s SATA, which can
    send about 300 megabyte/s. from the buffer to the
    computer, and it is rapidly increasing everyday.
  • RPM Rotation per Minute.

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Characteristics
  • Seek time currently ranges from just under 2 ms
    for high-end server drives, to 15 ms for
    miniature drives, with the most common desktop
    type typically being around 9 ms. There has not
    been any significant improvement in this speed
    for some years.
  • Ms Millisecond.

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Characteristics
  • Shock resistance is especially important for
    mobile devices. Some laptops now include a motion
    sensor that parks the disk heads if the machine
    is dropped,

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Characteristics
  • Latency also known as rotational delay time.
    The time it takes to access a particular location
    in storage from the initial position. The lower
    the latency, the faster the hard disk drive.

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Optical Disk
  • Optical storage is referring to the storage of
    data on an optically readable medium. Data is
    recorded by making marks in a pattern that can be
    read back with the aid of light.
  • A common modern technique used by computers
    involves a tiny beam of laser light precisely
    focused on a spinning disc.

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Optical Disk
  • Unlike magnetic disks having several concentric
    tracks, an optical disk has one long track
    starting at the outer edge and spiraling inwards
    to the centre.

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CD-ROM, CD-R, CD-RW
  • CD-ROM- Compact Disk Read Only Memory.
  • CD-R- Compact Disk Recordable. Write once read
    more.
  • CD-RW- Compact Disk Read Write. For Re-Writing
    many times

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  • CD, CD-ROM Read only storage, used for mass
    distribution of digital information (music,
    video, computer programs)
  • CD-R Write once storage, used for tertiary and
    off-line storage
  • CD-RW Slow write, fast read storage, used for
    tertiary and off-line storage
  • Ultra Density Optical or UDO is similar in
    capacity to BD-R or BD-RE and is slow write, fast
    read storage used for tertiary and off-line
    storage.

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Blu-ray
  • Blu-ray is a newer optical disc storage media
    format. Its main uses are high-definition video
    and data storage. The disc has the same
    dimensions as a CD or DVD. The term "Blu-ray"
    comes from the blue laser used to read and write
    to the disc. The Blu-ray discs can store much
    more data then CDs or DVDs. A dual layer Blu-ray
    disc can store up to 50GB, almost six times the
    capacity of a dual layer DVD (WOW!). Blu-ray
    discs have similar devices used to read them and
    write to them as CDs have. A BD-ROM drive can
    only read a Blu-ray disc and a BD writer can read
    and write a Blu-ray disc.

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An old 4x CD-ROM Drive.
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Characteristics
  • Capacity
  • A standard 120 mm, "700 MB" CD-ROM can hold about
    847 MB of data.
  • In comparison, a single-layer DVD-ROM can hold
    4.7 GB of error-protected data, more than 6
    CD-ROMs.

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  • Transfer rates
  • As of 2004, the fastest transfer rate commonly
    available is about 52x or 10,350 rpm and 7.62
    megabytes per second.
  • 1x or 1-speed which gives a data transfer rate
    of 150 kilobytes per second in the most common
    data format.

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  • CD-Recordable drives are often sold with three
    different speed ratings, one speed for write-once
    operations, one for re-write operations, and one
    for read-only operations. The speeds are
    typically listed in that order ie a 12x/10x/32x
    CD drive can, CPU and media permitting, write to
    CD-R discs at 12x speed (1.80 MB/s), write to
    CD-RW discs at 10x speed (1.50 MB/s), and read
    from CD discs at 32x speed (4.80 MB/s).

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  • The 1x speed rating for CD-ROM (150 kB/s) is
    different than 1x speed rating for audio CD
    (172.3 kB/s) and is not to be confused with the
    1x speed rating for DVDs (1.32 MB/s).

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DVD
  • DVD (also known as "Digital Versatile Disc" or
    "Digital Video Disc") is a popular optical disc
    storage media format. Its main uses are video and
    data storage. Most DVDs are of the same
    dimensions as compact discs (CDs) but store more
    than six times as much data.

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  • DVD-ROM has data that can only be read and not
    written,
  • DVD-R and DVDR can record data only once and
    then function as a DVD-ROM.
  • DVD-RW, DVDRW and DVD-RAM can both record and
    erase data multiple times.

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Internal mechanism of a DVD-ROM Drive.
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Memory StorageDevice
  • Pen Drive/USB Drive/Flash Drive
  • It is a plug and play (PnP) device that simply
    connects into a USB port of a computer.
  • One can read, write, copy, delete and move data
    from it to computers HDD or from HDD to pen
    drive.
  • One can even run application like MP3 files or
    music video directly from it.

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Pen Drive
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Memory StorageDevice
  • Memory Card (SD/MMC)
  • Flash memory based cards are removable storage.
  • in addition to computer, These cards are used in
    digital camera, cell phone etc.
  • SD Secure Digital
  • MMC Multimedia Card.

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Online Storage
  • Internet Can also be a Source of Storage.
  • www.atbackup.com
  • www.connected.com
  • www.mcafee.com
  • www.shii.com

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