10/5: Data storage concepts

1. 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.

2. 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,

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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