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 disks 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 a mplification 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

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) 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