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					       Storage Devices

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

               IN PUT                 PROCESSOR    OUTPUT




                                      PERMAN ENT
                                       STORAGE




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



Rick Graziani graziani@cabrillo.edu                         2
Cost v.s. Speed




Rick Graziani graziani@cabrillo.edu   3
Direct Access Devices vs. Sequential Access

Analogy:
• Record/CD vs. Cassette Tape




Rick Graziani graziani@cabrillo.edu           4
   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




Rick Graziani graziani@cabrillo.edu                                    5
Reel to Reel Tape (9 Track Tape)




Rick Graziani graziani@cabrillo.edu   6
Using a Cartridge Tape Drive




Rick Graziani graziani@cabrillo.edu   7
Storing Data on Tape




Rick Graziani graziani@cabrillo.edu   8
Storing Data on Tape

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

   Advantages
   • inexpensive
   • durable
   • portable
   Disadvantages
   • slow access rate

   Primary Use
   Backing up “on-line” information
Rick Graziani graziani@cabrillo.edu                           9
Direct Access Devices

 Direct Access = The specific information is accessed directly

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




Rick Graziani graziani@cabrillo.edu                              10
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




Rick Graziani graziani@cabrillo.edu                                 11
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




 Rick Graziani graziani@cabrillo.edu    12
Recording information

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




Rick Graziani graziani@cabrillo.edu                               13
Magnetic Media is sensitive to:
  •     temperature
  •     magnets
  •     touch, smoke, dirt
  •     folding, bending, pressure




Rick Graziani graziani@cabrillo.edu   14
Hard Disk Drives

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




Rick Graziani graziani@cabrillo.edu                      15
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

 Rick Graziani graziani@cabrillo.edu   16
How data is stored on disks

    Hotel analogy




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

Rick Graziani graziani@cabrillo.edu             17
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)




Rick Graziani graziani@cabrillo.edu                      18
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)




Rick Graziani graziani@cabrillo.edu                                   19
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.

Example
Creating a new file
and saving an
existing file to disk




Rick Graziani graziani@cabrillo.edu                                            20
Fragmentation and Defragmenting




Rick Graziani graziani@cabrillo.edu   21
How data is physically stored on the
disk
   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.




Rick Graziani graziani@cabrillo.edu                             22
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)




Rick Graziani graziani@cabrillo.edu   23
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
   software.
• 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”



Rick Graziani graziani@cabrillo.edu                           24
How Data is Removed from Floppy disks and Hard disks


Who's in charge of deleting files?



Deleting a file:



Unerasing a file




Rick Graziani graziani@cabrillo.edu                    25
Recovering Data

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


Rick Graziani graziani@cabrillo.edu   26
Optical Disks - CD ROMs

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




Rick Graziani graziani@cabrillo.edu                        27
Pit = On
No Pit (Land) = Off




Rick Graziani graziani@cabrillo.edu   28
Optical Disks - CD ROMs
   Advantages of CD ROM over magnetic disks
   • capacity and durability

   Disadvantage
   • WORM

   Read Only Drives and Read/Write CD ROM Drives

   Capacity
   • currently = 650 MB


Rick Graziani graziani@cabrillo.edu                29
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
  speeds.

 Rick Graziani graziani@cabrillo.edu   30
http://www.computerhope.com/help/cdrom.htm

• OTHER CD TECHNOLOGIES
• 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.
Rick Graziani graziani@cabrillo.edu                                          31
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
    channels.
•   Up to 32 subtitle/karaoke tracks.
•   Multilingual identifying text for title name, album name, song name, actors,
    etc.
•   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
    playback).
•   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).
Rick Graziani graziani@cabrillo.edu                                                  32
Disk Cartridges

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

Uses
• same as floppy or tape

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



Rick Graziani graziani@cabrillo.edu                       33
Flash Drives

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




Rick Graziani graziani@cabrillo.edu   34
       Storage Devices

CS 1 Introduction to Computers and Computer
                 Technology
                Rick Graziani
                   Fall 2004

				
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