10/5: Data storage concepts

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10/5 Data storage concepts

• What is data storage?
• Types of storage
• magnetic, optical, magneto-optical, solid state
• Storage characteristics
• Magnetic storage
• Floppy disks
• Hard disk drives
• Optical storage
• CD-ROMs, etc.
• DVDs, etc.

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Data storage what is it?

• Long-term storage, not immediate memory
• Not RAM (short-term memory)
• Synonyms secondary storage, auxiliary storage,
  mass storage

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imation.com,
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Data storage where is it?

• Storage involves 2 parts the device the media
• Removable vs. fixed media
• Where can you store data?
• magnetic media
• optical media
• magneto-optical media
• solid state media

image courtesy of How Computers Work
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Storage characteristics

• Random vs. sequential access
• Tracks sectors
• Speed
• spin rate (RPM)
• seek time latency
• access time
• data transfer rate
• Storage Capacity
• areal density
• size

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Magnetic data storage

• Use magnets to store bits
• example 0 N , 1 S
• Reading and writing
• Floppy disk drives
• Hard disk drives

PACE
image courtesy of How Computers Work
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Floppy disk drives types

• Low-density floppy drives 5.25 floppy
  disks3.5 1.44 MB floppy disks
• High-density floppy drives Zip disks, LS-120
  disks

Images courtesy of How Computers Work,
Imation.com, and Iomega.com
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Floppy disk drives how they work

• Shutter opens with an arm.
• Cookie spins on the spindle.
• Read/write heads get close to the cookie inside
• Magnetic particles generate electric currents in
  the heads.
• Electric currents are interpreted as a series of
  bits.

Images courtesy of How Computers Work
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Hard disk drives overview

• Glass platters coated with magnetic particles
• Read/write heads like floppy drives but much
  smaller
• Multiple platters, multiple heads.

Image courtesy of How Computers Work
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Hard disk drives how they work

• Platters spin on the spindle.
• Heads move over the platters.
• To read, magnetic particles generate currents in
  the heads.
• Electric currents are interpreted as a series of
  bits.
• To write, the electric currents manipulate the
  magnetic particles on the platters.

Images courtesy of How Computers Work
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Optical Storage

• Instead of using magnetism to store bits, we use
  light
• A laser is the light
• Laser light amplification by stimulated
  emission of radiation
• Extremely focused, narrow beam of powerful light
• Depending on the wavelength, the beam can be
  narrower or wider
• Lands are flat areas on the disc
• Reflect light like a mirror
• Pits are holes in the disc
• Scatter light

Courtesy of http//www.microserve.net/tpetchy/DVD
.shtml
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CD Drives Types and Operation

• CD-ROM drive speeds how many times faster than
  the original CD-ROM drives
• 2x, 4x, 6x, 8x, 16x, 32x, 48x
• Operation
• Diode generates laser
• Laser bounces off mirrors, reaching the disc
• Disc reflects or scatters laser
• Light-sensing diode sees the reflections,
  comparing them to a timing circuit to generate 0s
  and 1s

Image courtesy of c-cube.com
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Types of Optical Discs

• Compact discs
• CD-ROM read only memory (680 MB)
• CD-R Recordable (650 MB)
• CD-RW ReWritable (495 MB)

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Types of Optical Discs

• Digital versatile discs higher density storage
• DVD-ROM read only memory (4.7 17 GB)
• DVD-R Recordable (3.9 GB?)
• DVD-ram (5.2 GB) DVDRW (6.0 GB) Rewritable
  (still fighting)

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