Transcript 10/8: Data storage concepts

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.
Data storage: what is it?
• Long-term storage, not immediate memory
• Not RAM (short-term memory)
• Synonyms: secondary storage, auxiliary storage,
mass storage
images courtesy of dalelabs.com,, iomega.com, imation.com,
Data storage: where is it?
• Storage involves 2 parts:
the device & the media
• Removable vs. fixed
media
• Where can you store
data?
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magnetic media
optical media
magneto-optical media
solid state media
image courtesy of How Computers Work
Storage characteristics
• Random vs. sequential access
• Tracks & sectors
• Speed
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spin rate (RPM)
seek time & latency
access time
data transfer rate
• Storage Capacity
– areal density
– size
Image courtesy of How Computers Work
Magnetic data storage
• Use magnets to store bits:
– example: 0 = N , 1 = S
• Reading and writing
• Floppy disk drives
• Hard disk drives
image courtesy of How Computers Work
PACE
Floppy disk drives: types
• Low-density floppy drives:
5.25” floppy disks
3.5” 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
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
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
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
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
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:
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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
Types of Optical Discs
• Compact discs:
– CD-ROM: read only memory (680 MB)
– CD-R: Recordable (650 MB)
– CD-RW: ReWritable (495 MB)
Image courtesy of c-cube.com
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) & DVD+RW (6.0 GB): Rewritable
(still fighting)
Image courtesy of c-cube.com