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?– 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– 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
PACE
image courtesy of How Computers Work
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
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:• 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)
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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) & DVD+RW (6.0 GB): Rewritable
(still fighting)
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