2. Magnetic Disks Floppy drive and disk Portable 3.5 inch disc with a limited capacity of 1.4 Mb. Zip drive and disk Slightly larger and more durable version of a floppy disc. Can store up to 750 Mb and has a faster access time .
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6. Optical Drives The information is recorded onto the disk in the form of pits and lands. Pits are raised, lands are lowered. Optical technologies involving the use of lasers have contributed to the production of CD and DVD drives. Land Pit
7. Optical Drives The drive uses a lower powered laser to scan the disk as it turns. The light is reflected from the pits and lands, on the disc surface, differently and it is this pattern of reflection that indicates the data read.
8. Optical Media CD-ROM A CD-ROM disk is a read only medium whose contents cannot be altered once data is written to it. Capacity of a CD is approximately 700Mb CD-R CD-R drives allow CD-ROMs and audio CDs to be written to, but only one time.
9. Optical Media CD-RW (ReWritable) CD-RW drives enable CDs to be written onto it in multiple sessions . DVD-R, DVD-RW, DVD+R, DVD+RW, DVD-RAM DVDs use an optical technology that uses a higher laser wavelength than CD. This means that tracks can be smaller and closer together and pits in the surface can be smaller. Capacity is either 4.7 or 8.4 Gb
10. Data Transfer Rates CD-ROMs 150 Kb/sec DVD-ROMs 1.32 Mb/sec This is the transfer rate for 1 x CD-ROMs / DVD-ROMs But most CD-ROMs / DVD-ROMs run faster than this e.g. 4 x, 32 x, 48 x
11. Data Transfer Rates CD-ROMs 150 Kb/sec DVD-ROMs 1.32 Mb/sec This CD-ROM is 52 x , so access rate is up to 52 x 150 Kb/sec = 7.8 Mb/sec
12. Blu-Ray Blu-Ray is the next generation of optical storage device It uses a narrower laser ( blue ) than the laser used for CD / DVD ( red ) Capacity is 27Gb or 54Gb Access speeds range from 4.5 Mb per second to 54Mb per second
13. Solid State Devices Made from Electrically Erasable Programmable Read-Only Memory ( EEPROM ) Physically very small and portable No moving parts therefore not damaged by movement Capacities are now increasing to 512 Gb May well replace hard disk drives in computers
