Ch 6:Secondary Storage

1
6
Secondary Storage
2
Objectives

• Describe todays standard floppy disk and compare
  it to Zip, SuperDisks, and HiFD disks.
• Describe the following kinds of disks internal
  hard disks, hard-disk cartridges, and hard-disk
  packs.
• Describe ways to improve hard-disk operations
  disk caching, redundant arrays of inexpensive
  disk, and data compression.
• Compare the CD and DVD formats.
• Describe the different types of optical disks.
• Describe other kinds of secondary storage
  magnetic tape, Internet drives, and solid state
  storage.

3
Secondary Storage

• Can be used to save information.
• Holds information external from the CPU.
• Allows you to store programs, data, and
  information permanently.

4
Secondary Storage

• Review concepts of temporary storage (RAM)
  studied in chapter 4
• RAM (main memory) is temporary or internal
  storage.
• It has a storage capacity that is usually
  measured in megabytes.
• If power to the computer is turned off,
  everything in RAM disappears.
• This type of storage is said to be volatile.

5
Secondary Storage

• the concepts of permanent storage
• Secondary storage is permanent or external
  storage.
• It has a larger storage capacity and newer
  computers may have many gigabytes of storage.
• If power to the computer is turned off,
  everything on secondary storage remains intact.
• This type of storage is said to be nonvolatile.

6
Floppy Disks

• Removable
• Write-protect
• Parts
• Tracks
• Sectors

7
Floppy Disks

• Parts of a floppy disk
• Shutter slide metal component that opens when
  disk is inserted into drive (read-write area).
• Write-protect notch when opened, prevents data
  from being written to the disk.
• Tracks closed concentric circles on the disk
  invisible to the eye.
• Sectors wedge-shaped sections on the disk
  invisible to the eye.

8
Floppy Disks

• Floppy disks are portable, removable storage
  media.
• They are also known as diskettes, disks, flexible
  disks, and floppies.
• They are flat circular pieces of Mylar plastic
  that rotate within a jacket.

9
Floppy Disks

• They are used to store programs and data
  permanently.
• Data is stored as electromagnetic charges on a
  metal oxide film coating the mylar plastic.
• The presence or absence of the charges (2-state
  binary code) represents data.
• Data is read from, or written to the disk,
  through the read-write head in the disk drive.

10
Floppy Disks

• Todays standard floppy disk 1.44 MB 3 ½ inch
  disk.
• Typically labeled 2HD - which means two-sided,
  high density.
• This disk can store 1.44 megabytes of data
  equivalent of 400 typewritten pages.

11
Floppy Disks

• Has thin exterior jacket made of hard plastic to
  protect the flexible disk inside.
• Has a shutter that slides open to expose the disk
  surface.
• Read-write head from the disk drive moves across
  the exposed disk to store and retrieve data.
• When the notch is open, data cannot be stored on
  the disk.

12
Floppy Disks

• Tomorrows standard floppy disks floppy-disk
  cartridges
• These are 3 ½ inch disks that are thicker and
  require special disk drives.
• The three best known floppy-disk cartridges are
• Zip Disks
• Produced by Iomega.
• Have a 100 MB or 250 MB capacity (over 170 times
  as much as todays standard floppy).
• Zip drives are standard on many of todays more
  powerful system units.
• Disadvantage - Cannot read and store data on 1.44
  MB standard disk.

13
Floppy Disks

• SuperDisks
• Produced by Imation.
• Have a 120 MB capacity.
• Advantage - Can read and store data on 1.44 MB
  standard disk.
• HiFD Disks
• From Sony Corporation.
• Have a 200 MB capacity (greater than SuperDisk).
• Advantage Can read and store data on 1.44 MB
  standard disk.

14
Hard Disks

• A hard disk is another type of permanent storage.
• Hard disks use thick, ridged metallic platters as
  their storage media.
• They are able to store and retrieve information
  much faster than floppy disks.
• They have a greater storage capacity than floppy
  disks.

15
Hard Disks

• Hard Disk Crash
• The read-write head of a hard disk drive rides on
  a cushion of air about 0.000001 inches thick.
• The cushion of air is so thin that certain
  circumstances make the disk vulnerable to data
  loss.
• Smoke particles, fingerprints, dust, or human
  hair can come between the read-write head and the
  magnetic disk surface.
• This could cause some or all of the data on the
  disk to be destroyed and is referred to as a disk
  head crash.

16
Hard Disks

• Internal Hard Disk
• also known as a fixed disk
• located inside the system unit and cannot be
  removed
• has one or more metallic platters sealed inside a
  container called the disk drive
• contains the motor for rotating the disks, access
  arms, and read-write heads for every platter
• typical hard drive is composed of four 3-½ inch
  metallic platters
• Advantages over floppy
• capacity and speed
• Can hold as much information as 56,000 standard
  floppy disks

17
Hard Disks

• Hard-Disk Cartridge
• easy to remove as a cassette from a videocassette
  recorder.
• used primarily to complement an internal hard
  disk
• particularly useful to protect or secure
  sensitive information
• provide a computer with an unlimited amount of
  permanent storage.
• typical capacity is 2 gigabyte per cartridge.

18
Hard Disks

• Hard-Disk Pack
• composed of several platters aligned one above
  the other
• pack can be removed from the computer
• has access arms with two read-write heads, to
  read the surface above one, and one below
• used to store a massive amount of information
• used by banks and credit card companies to record
  financial information
• provide a computer with an unlimited amount of
  permanent storage.

19
Computer Access Time

• It is the time between the computers request for
  data from secondary storage and the completion of
  the data transfer.
• The time factor between the computers request
  for data from secondary storage and the
  completion of the data transfer.

20
Hard Disk Performance

• There are three ways to improve the performance
  of hard disks
• Disk Caching
• Disk caching improves performance by anticipating
  data needs.
• It requires a combination of hardware and
  software.
• Frequently used data is read from the hard disk
  into cache memory during idle processing.
• Data is then accessed directly from cache memory
  to RAM memory when needed.
• The transfer rate from cache memory is faster
  than from the hard disk.
• System performance can increase as much as 30
  percent using disk caching.

21
Hard Disk Performance

• RAIDs (Redundant Arrays of Inexpensive Disks)
• RAIDs are inexpensive hard-disk drives grouped
  together using networks and special software.
• They improve hard disk performance by expanding
  external disk storage.
• The grouped disks are treated as a single
  large-capacity hard disk.
• RAIDs can outperform single disks of comparable
  capacities.

22
Hard Disk Performance

• File Compression
• File compression can increase storage capacity by
  reducing the amount of space required to store
  data and programs.
• File compression can be used with hard or floppy
  disks.
• It helps to speed the transmission of files from
  one computer to another.
• It is the common file transfer activity over the
  Internet.
• File compression replaces repeated bit patterns
  with a token symbol to reduce space.
• Files can be shrunk to a quarter of original size
  using file compression.
• Files can be decompressed back to original file
  with decompression software.

23
Optical Disks

• Permanent storage media that use laser technology
  to store data
• The laser is used to alter the surface of a
  plastic or metallic disk to represent binary
  code.
• Flat areas (lands) and bumpy areas (pits) on the
  disk surface represent the 0s and 1s.
• The disk is then read by a laser that projects a
  tiny beam of light on these areas.

24
Optical Disks

• Optical disks can be 3½, 4¾, 5¼, 8, 12 and 14
  inches.
• Most common size of optical disk is 4¾ inch.
• Optical disks can typically hold over 17
  gigabytes of data (several million typewritten
  pages).
• There are two common formats of optical disks
• CD (Compact Disc)
• DVD (Digital Versatile Disc or Digital Video Disc)

25
Compact Disc Features

• CDs are the most widely used optical disk format.
• This format can store 650 megabytes of data on
  one side of the disk.
• Its rotation speed determines how fast data can
  be transferred from the disk.
• Examples
• 24X 3.6 MB per second
• 32X 4.8 MB per second

26
CD-ROM

• The three basic types of CDs are
• CD-ROM (Compact Disc-Read Only Memory)
• Similar to a commercial music CD.
• Cannot be written on or erased by user.
• Used to distribute large databases and references.

27
CD-R CD-RW

• CD-R (Compact Disc-Recordable)
• Can be written to once but read many times.
• Also known as WORM (Write Once, Read Many times).
• Used to archive or permanently store large
  amounts of information.
• Used to create custom music CDs (see Making IT
  Work for You CD-R Drives and Music from the
  Internet) and to archive data.
• CD-RW (Compact Disc-Rewriteable)
• Also known as erasable optical disk.
• Disk surface is not permanently altered when data
  is recorded.
• Can be written on, erased, and then written on
  again.
• Used to create and edit multimedia presentations.

28
DVD

• DVDs are also known as Digital Video Disc.
• They can store 17 gigabytes on one side of the
  disk (more than 30x CD disk).
• Many DVD discs can store data on both sides of
  the disk, doubling the capacity.

29
DVD

• DVD-ROM (Digital Versatile Disc-Read Only Memory)
• Cannot be written on or erased by user.
• Can provide over two hours of very high quality
  video and sound.
• DVD-R (Digital Versatile Disc-Recordable)
• Can be written to once but read many times.
• Used to create permanent archives for large
  amounts of data.
• Not as widely used as CD-R discs because of their
  higher costs.
• DVD-RAM (Digital Versatile Disc-Random Access
  Memory) and DVD-RW (Digital Versatile
  Disc-Rewriteable)
• Two types of reusable DVD disks.
• They can be used over and over again on a variety
  of applications.

30
DVD

• DataPlay
• This is a new optical disk the size of a quarter.
• It has a capacity of 500 MB.
• This disk is capable of holding five hours of CD
  quality sound.
• It will become widely used for specialized
  applications such as storing digital photographs
  and music for portable players.

31
Magnetic Tape

• Form of permanent storage media
• Stores data in sequential access only, that is,
  one after another
• Once data is stored on tape, access to the data
  is always sequential, starting at the beginning
  of the tape and working through until the data is
  found.
• Sequential access takes more time to access
  specific information.
• Magnetic tape is almost exclusively used for
  backup purposes today.

32
Magnetic Tape

• There are two forms of magnetic tape storage
• Magnetic Tape Streamers used with
  microcomputers.
• Magnetic Tape Reels used with minicomputers and
  mainframes.

33
Magnetic Tape

• Internet Hard Drives
• These are also known as idrive or online storage.
• They provide users with free or low-cost storage.
• A user can access stored information from any
  computer connected to the Internet
• They are typically used as a specialized
  secondary storage device.
• Not for storing highly personalized or sensitive
  information.

34
Magnetic Tape

• Solid-State Storage
• Solid state has no moving parts.
• Information is stored and retrieved
  electronically.
• This storage is more expensive than other storage
  but is also more reliable and requires less
  power.
• Flash memory cards are solid-state storage
  devices used in notebook computers.
• Flash memory is used in specialized input devices
  to capture and transfer data to desktop
  computers. Examples of uses are storage and
  transfer of digital camera images and recording
  and transfer of MP3 music files.