Magnetic Storage Concepts

1
Magnetic Storage Concepts

• How Computers Use Magnets

2
Lesson Objectives

• Introduce magnetism as a memory tool
• Motivate the need for efficient permanent
  memory
• Demonstrate the ability to magnetize
• Demonstrate the use of magnetism to store
  information
• Reinforce the idea that computers speak binary,
  requiring us to encode and decode
• Introduce the topic of electro-magnetism

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Memory Types

• Short-term memory is used for things that you
  probably will need to use soon
• Humans use their index cards, mnemonics, etc.
• Computers use RAM and caches
• Long-term memory is for things may not need for a
  long time but dont want to forget
• Humans use notebooks, reference books, libraries,
  audio tape, video tape, etc.
• Computers use floppy disks, hard disks, CDs, etc.

4
Disk Anatomy

• Floppy disks contain a circular piece of plastic
  embedded with millions of elements of magnetic
  material
• Hard disks are similar but consist of hard
  platters holding the magnetic elements
• Both types of disks are divided into tracks which
  are further divided into sectors
• Both have read/write heads on arms that are
  positioned based on addresses

5
Why Use Magnets?

• Magnetic material is readily available and
  therefore relatively cheap
• It can also be formed into many shapes
• We can work with very small magnets
• Magnets hold state extremely well
• In summary, magnets
• Dont take up much space
• Dont cost much
• Are reliable
• And can be written to and read from quickly

6
Making Magnets

• A ferromagnetic material (such as iron or steel)
  can be magnetized by exposing it to a magnetic
  field
• If its magnetic domains align and stick, it
  becomes a permanent magnet
• It now has north and south poles
• It also emits a magnetic field which can be read

7
Exercise

• Encode your groups letter using the attached
  chart
• Magnetize bits by rubbing them with your
  permanent magnet 20 40 times
• Test each bit by trying to pick up a paper clip
• Read and decode your neighbors letter
• Write their letter on the board

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Exercise Objectives

• Learn how to magnetize an object and use that
  property to hold state information
• Encode to store information in binary and decode
  to read it back
• Appreciate the importance of maintaining place
  order

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Improvement Opportunities

• RAM vs. disk
• Optical storage

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Lesson Summary

• Computers use magnetism for fairly fast, pretty
  cheap, long-term storage
• Magnetic material can be magnetized by exposing
  it to a strong magnetic field
• Floppy and Hard Disks consist of millions of tiny
  elements that can be magnetized
• Computers store data permanently by magnetizing
  and demagnetizing these elements