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

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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

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

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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

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

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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) & DVD+RW (6.0 GB): Rewritable

(still fighting)

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