Magnetic Media - PowerPoint Prese by pengxiang


									       Storage Devices

CS 1 Introduction to Computers and Computer
                Rick Graziani
                   Fall 2004
Permanent Storage

               IN PUT                 PROCESSOR    OUTPUT

                                      PERMAN ENT

• What is in charge of permanent storage
•   The operating system software!

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Cost v.s. Speed

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Direct Access Devices vs. Sequential Access

• Record/CD vs. Cassette Tape

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   Sequential Access Devices
   Sequential Access = In order to access specific information, the
     device must sequentially pass through all preceding information
   • 9 Track Tape (Reel to Reel)
   • Cartridge Tapes

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Reel to Reel Tape (9 Track Tape)

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Using a Cartridge Tape Drive

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Storing Data on Tape

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Storing Data on Tape

   Recording information
   • Bits are recorded as positive and negative polarity on
     magnetic tape (“magnetic media”)

   • inexpensive
   • durable
   • portable
   • slow access rate

   Primary Use
   Backing up “on-line” information
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Direct Access Devices

 Direct Access = The specific information is accessed directly

 • floppy disk drives
 • hard disk drives
 • cartridge disk drives
 • CD ROM and DVD drives

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Floppy Disks

Floppy Disk = iron oxide coating on a portable mylar plastic disk

Becoming obsolete

Old 5 1/4 inch diskettes (FYI)
• double density = 360K capacity
• high density = 1.2 MB capacity

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Floppy Disks

Newer 3 1/2 inch diskettes
• double density = 720K capacity
• high density = 1.4 MB capacity
(Right drive for the right densities)

Advantages of 3 1/2 inch
• size, capacity, speed, durability

Notch with slide = write protection
• closed = Read/Write
• open = Read Only

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Recording information

   •     Bits are recorded as positive and negative polarity on
         magnetic tape (“magnetic media”)

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Magnetic Media is sensitive to:
  •     temperature
  •     magnets
  •     touch, smoke, dirt
  •     folding, bending, pressure

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Hard Disk Drives

   Hard Disk = Iron oxide coating on one or more rigid
     aluminum disks called platters

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Hard Disk Drives

Common Sizes
Older Disks
• 5 MB, 10 MB, 20 MB, etc.
Newer Disks
• 50 GB and more!
• Smaller, cheaper and faster!

Advantages of Hard Disk Drives
  over Floppy Disk Drives
• more capacity
• faster access

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How data is stored on disks

    Hotel analogy

• What is in charge of storing information
    on the hard disk drive (and other storage
•   The operating system software!

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How data is stored on disks

   track = a series of concentric rings on the disk
   • A track is divided into several sectors
   (track) sector =a section of a track which stores a
      predetermined number of bytes (bits)

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How data is stored on disks

   Several sectors are combined to create clusters or blocks
   cluster (Windows and Macs) or block (UNIX) = The number of
      sectors which is allocated on the disk each time a file needs
      space on the disk.
   Windows 95 (later versions) and Windows 98 using FAT32
    1 cluster = 8 sectors (4K bytes)
    Recognizes disk drives up to 2 terabytes (2 trillion bytes)

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How data is stored on disks

FAT (File Allocation Table) and Directory = A file, a table, which is
  found on one of the first sectors of every diskette and hard disk drive
  (created when the disk is formatted), and contains information
  regarding every file stored on that disk including the file name, the
  date and time that file was created or modified, the size of the file, and
  which sectors are allocated for that file.

Creating a new file
and saving an
existing file to disk

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Fragmentation and Defragmenting

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How data is physically stored on the
   Read/Write Heads = Part of disk drive which skims the
     disk (ten millionths of an inch) in order to retrieve or
     store information.
   Disk Crash or Head Crash = When the R/W head
     touches the disk.

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Formatting a disk

 Q: Why do we format a disk and
    what actually does it?
 A: We format a disk so it can be
    used by the operating system
    software. The operating system
    software does the formatting of
    the disk.

 Q: How does the operating system
    do it?
 A: There is a operating system
    software file (program) which
    does the formatting. (CPU/RAM)

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Formatting a disk

What does formatting a disk do?
1. Erases all of the information on the disk
2. Prepares disk to be used by the operating system
• divides tracks into sectors
• determines cluster size
• creates a file allocation table (FAT) or similar table on
   other operating systems
3. Optional: Copies operating system files to this disk in
   order to make this a “boot disk”

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How Data is Removed from Floppy disks and Hard disks

Who's in charge of deleting files?

Deleting a file:

Unerasing a file

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Recovering Data

•   Norton Utilities™
     – Optimizes and
       defragments files for
       faster hard drive
     – Detects and fixes many
       Windows® and disk
       problems automatically.
     – Can monitor your PC
       continuously to spot
       problems before they

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Optical Disks - CD ROMs

Recording bits of data
• Data is permanently recorded by a laser beam on a disk
• WORM = Write Once Read Many

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Pit = On
No Pit (Land) = Off

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Optical Disks - CD ROMs
   Advantages of CD ROM over magnetic disks
   • capacity and durability

   • WORM

   Read Only Drives and Read/Write CD ROM Drives

   • currently = 650 MB

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Optical Disks - CD ROMs

What are CD ROMs good for?
• graphics, videos, games,
  software, (backups)

Speed of CD ROM Drives
• 4x, 6x, 8x, 10x, etc.
• larger the number, faster the
  transfer speed from the CD
  ROM to RAM

What’s next?
• Need more capacity and faster

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• CD-R - (CD Recordable) Drive which you are able to write to once.
    Once the drive is written to it cannot be erased.
    CD-RW - (CD ReWritable) drive which is a popular alternative to the
    CD-R drive. CD-RW has the capability of being written to at least one
    thousand times. The drawback with CD-RW diskettes is with the lower
    reflectivity of the disc itself can limit the readability. Many CD-ROM and
    CD-R drives may have a difficult time reading these disks.
    DVD - (Digital Versatile Disc) New standard released in 1995 which
    originally was called Digital Video Disc was later changed to Digital
    Versatile Disc. DVD offers an initial storage capacity of 4.7GB (of
    digital information on a single-sided, single-layer disc the same
    diameter and thickness of a current CD-ROM.
    DVD-RAM - ReWritable drive type that uses a phase-change
    technology like the CD-RW drives. However , DVD-RAM discs cannot
    be read by standard DVD-ROM drives because of the differences in
    both reflectivity of the medium and the data format.
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What are the features of DVD-Video?
•   Over 2 hours of high-quality digital video (over 8 on a double-sided, dual-
    layer disc).
•   Support for widescreen movies and standard or widescreen TVs (4:3 and
    16:9 aspect ratios).
•   Up to 8 tracks of digital audio (for multiple languages), each with up to 8
•   Up to 32 subtitle/karaoke tracks.
•   Multilingual identifying text for title name, album name, song name, actors,
•   Automatic "seamless" branching of video (for multiple story lines or ratings
    on one disc).
•   Up to 9 camera angles (different viewpoints can be selected during
•   Menus and simple interactive features (for games, quizzes, etc.).
•    "Instant" rewind and fast forward, including search to title, chapter, track,
    and timecode.
•   Durability (no wear from playing, only from physical damage).
•   Not susceptible to magnetic fields. Resistant to heat.
•   Compact size (easy to handle and store, players can be portable).
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Disk Cartridges

Disk Cartridges = portable disks which store almost as
  much information and is almost as fast as a hard disk

• same as floppy or tape

Iomega Zip Drive = 100 MB
Iomega Jaz Drive = 1 GB

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Flash Drives

•   Capacity
     – 64 MB
     – 128 MB
     – 256 MB
     – 512 MB
     – 1 GB
     – And more
•   $35 to $175

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       Storage Devices

CS 1 Introduction to Computers and Computer
                Rick Graziani
                   Fall 2004

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