CS101 Lecture Supplement for Lecture 8

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CS101 Lecture Supplement for Lecture 8

• On Your Own Storage Devices

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Everything is zeros and ones

• When a computer is running the zeros and ones are
  moving around in electronic form
• What happens when the power is turned off?
• For the zeros and ones to survive they must be
  placed on a storage device

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What are good characteristics of storage devices?

• Fast
• Usually using a storage device is the slowest
  thing a computer does
• Random Access (can get to anything anytime)
• CD Random Access
• Cassette Tape ? Random Access
• Reliable
• Need zeros and ones to be there when needed
• Cheap

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There are 3 main types of storage

• Magnetic, Optical, and Flash
• For each type of storage we will learn
• What types of devices use that storage method
• How it stores zeros and ones
• What is its advantages
• What is its disadvantages

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Magnetic Storage

• Types of magnetic storage devices
• Hard Drive
• Floppy Disk
• Zip Disk
• Tape Drive
• Cassette Tape Drive
• etc

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How magnetic storage works

• A magnetic disk contains a metal platter which is
  coated with tiny particles of ferromagnetic
  material (usually iron oxide ).
• A ferromagnetic material is a material that can
  hold a magnetic charge.
• To copy zeros and ones on to a disk a read/write
  head passes over the tiny ferromagnetic particles
  and either aligns the particles with a positive
  polarity (equals a 1) or a negative polarity
  (equals a 0)
• To read zeros and ones off a disk the read/write
  head passes over the tiny ferromagnetic particles
  and reads their polarity (positive equals 1 and
  negative equals 0)

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Hard Drive Most Important Magnetic Storage Device

• Most computers use a hard drive to store all
  their information
• Most computers use hard drives because they do
  all four things fairly well. Hard drives
• are the fastest of the three types of storage
  devices
• have random access
• are very reliable
• are relatively cheap

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Optical Storage

• Types of optical storage
• CD
• DVD
• HD-DVD (Discontinued by Toshiba)
• Blu-Ray DVD
• Sony Mini Disk
• Laser Disk
• etc

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How optical storage works

• A disk (mostly CDs or DVDs for computers) is
  placed in the drive. The disk is spun in the
  drive. As the disk is spun a laser is pointed at
  the bottom of the disk. If the laser reflects
  off the bottom of the disk it is a 1. If the
  laser does not reflect off the bottom of the disk
  then it is a 0.

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Reflected or Not Reflected

• How the laser is reflected, or not reflected, is
  the difference between the different types of CD
  and DVD disks and drives
• 3 Different types of CD and DVD drives
• ROM Read Only Memory
• R Recordable
• RW Recordable and Rewriteable

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ROM Bumps or No Bumps

• CD and DVD ROMs can only be read from. You
  cannot copy data to a ROM disk
• ROM disk surfaces have bumps or no bumps to
  reflect the laser back or not reflect the laser
  back

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R Dye or No Dye

• CD-R works by replacing the aluminum layer in a
  normal CD with an organic dye compound. This
  compound is normally reflective, but when the
  laser focuses on a spot and heats it to a certain
  temperature, it "burns" the dye, causing it to
  darken. When you want to retrieve the data you
  wrote to the CD-R, the laser moves back over the
  disc and thinks that each burnt spot is a bump.
  The problem with this approach is that you can
  only write data to a CD-R once. After the dye has
  been burned in a spot, it cannot be changed back.

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CD-ROM CD-R
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RW Phase Change

• RW uses phase change to represent zeros and ones.
  Phase change relies on a very special mixture of
  antimony, indium, silver and tellurium. This
  particular compound has an amazing property When
  heated to one temperature, it crystallizes as it
  cools and becomes very reflective when heated to
  another, higher temperature, the compound does
  not crystallize when it cools and so becomes dull
  in appearance.

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How a RW drive works

• RW drives have three laser settings to make use
  of this property
• Read - The normal setting that reflects light to
  the optoelectronic sensor
• Erase - The laser set to the temperature needed
  to crystallize the compound
• Write - The laser set to the temperature needed
  to de-crystallize the compound
• You can change the compound 100,000 times before
  it loses its ability to change

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What about the X?

• What would CD-R x40 mean?
• If you see an x followed by a number after a
  drive type it just means the drive is that much
  faster then the original drive.
• A CD-R x40 drive can write CD-Rs 40 times faster
  then the original CD-R drives

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What about that other stuff?

• After some DVD drives you will see
• ROM
• R
• -RW
• RW
• RAM
• Dual Layer
• If just means the drive can do all of those
  thisngs
• -RW, RW, and RAM are just different formats
  using the phase technology
• Buy a drive that can do all of them
• Super Multi-drive
• Blue Lazar will change things
• Smaller lazar so more zeros and ones can be on a
  disk
• HD Movies

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Optical Storage Used Mostly for Portability and
Multimedia

• Most multimedia is stored on optical disks
• Music, movies, etc
• Optical specializes in these areas because it
  does three things fairly well. Optical storage
• has random Access
• is very reliable
• is relatively cheap
• Optical storage is not the main storage in
  computers because it is to slow

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Flash Memory

• Types of Solid State Storage
• Solid State Hard Drive
• Up to 512 GBs
• Very expensive
• Flash Drives
• Type of drive needed by Lab 4
• Compact Flash Cards
• SD
• Memory Stick
• Compact Flash
• Etc
• MP3 players
• iPod Nano
• etc

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Why is flash memory sometimes called solid state?

• When an electronic device is called solid state
  it usually means there is no moving parts
• Usually more reliable then things with moving
  parts

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How does solid state work?

• In a solid state storage device zeros and ones
  are stored as trapped charges
• Over 50 charge 1
• Under 50 charge 0
• More complicated then we have time for in CS101
• The unique thing about solid state memory is that
  it can hold these charges without needing a
  constant supply of electricity and, of course, it
  can alter the charges without any moving parts

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Solid State Storage Used Mostly for Portability

• Solid State specializes in portability because it
  does three things fairly well. Solid State
  storage
• has random Access
• is very reliable
• is fast
• Solid State storage is not the main storage in
  computers because it is to expensive and does not
  have the large capacity of hard drives, but this
  is quickly changing