Magnetic Memory

1
Magnetic Memory
2
History

• Hard Disk Drives Invented 1950s
• Originally up to 20 inches in diameter
• Floppy Disk Drives - 1967

3
Applications

• Hard disk drive
• Floppy Disks
• Some Camcorders
• Cell phones/PDAs
• VCRs
• MP3 Players

4
How Does It Work?

• Theory is similar to how cassette tapes work
• Cassette tapes use a thin plastic base that is
  coated with a ferric oxide powder (Commonly Iron
  Oxide FeO)
• When this magnetic material is exposed to an
  electromagnet it has magnetic flux applied to it.
  The oxide powder remembers the lines of flux.
  In a hard disk drive these are recorded as binary
  digits of 0 or 1

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Advantages

• http//electronics.howstuffworks.com/cassette2.htm

• In a cassette-tape deck, the read/write head
  touches the tape directly. In a hard disk, the
  read/write head goes over the disk without
  touching.
• This advantage increases the performance of hard
  disk drives by lessening the seek time the time
  between which the CPU requests a file and when
  the first byte is sent to the CPU. Average seek
  time is 10-20 ms

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http//computer.howstuffworks.com/hard-disk6.htm

• The magnetic material on a cassette tape applied
  to a thin plastic strip. In a hard disk, the
  magnetic recording material is applied to a
  high-precision aluminum or glass disk. The
  hard-disk platter is then polished to mirror-type
  smoothness.
• This platter typically spins between 5600 7200
  rpm.

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http//computer.howstuffworks.com/hard-disk6.htm

• On a cassette tape you have to fast-forward or
  reverse to get to the desired point on the tape.
  This can take several minutes with a long tape.
  On a hard disk, you can move to any point on the
  surface of the disk almost instantly.
• The arm on the hard disk drive can move from the
  middle to the edge and back about 50 times per
  second

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http//computer.howstuffworks.com/hard-disk6.htm

• The tape in a cassette-tape deck moves over the
  head at about 2 inches (about 5.08 cm) per
  second. A hard-disk platter can spin underneath
  its head at speeds up to 3,000 inches per second
  (about 170 mph or 272 kph)!

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Advantages

• Magnetic memory can store/record quickly
• Can be erased and re-recorded as needed
• Can store large amounts of data in a small space

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Future Applications - MRAM

• Magnetoresistive Random Access Memory
• RAM (Random access memory) operates by using
  transistors and capacitors to make memory cells
  aligned in columns and rows in which information
  is stored. RAM is volatile depends on electricity
  flowing, therefore if power is taken away without
  info being saved to a hard drive the info is
  lost.
• MRAM operates more like a traditional hard drive
  but doesnt include any mechanical parts so
  therefore has even greater speed and durability.
• Made up of ferromagnetic plates called memory
  cells
• Reads info by measuring electrical resistance of
  a specific cell
• Faster write speeds, retains data after power
  supply is cut off

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References

• http//computer.howstuff works.com/hard-disk.htm
• http//en.wikipedia.org/wiki/Hard_disk_drive
• http//www.tfot.info/articles.php?itemId36/59/
• http//electronics.howstuffworks.com/cassette.htm