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Storage and Multimedia: The Facts and More Chapter 6
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Secondary Storage Device
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Secondary Storage Benefits Semi-permanent Non-volatile Reliable Convenient – Locate and access data quickly
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Secondary Storage Benefits Compressed storage Diskette – about 500 printed pages Optical disk – about 500 books Economy Savings in physical storage costs Savings in the speed and convenience of filing and retrieving data
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Types of Storage Magnetic Disk Storage Optical Disks CD-ROM CD-R CD-RW DVD-ROM Blu-ray Magnetic Tape Storage Flash Drive
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Magnetic Disk Storage Data represented as magnetic spots Magnetized spot = 1 Absence of a magnetized spot = 0 Read Converts the magnetized data to electrical impulses Write Converts electrical impulses to magnetized spots on disk
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Diskettes Low capacity – small files Portable Flexible Mylar coated with metallic substance Hard plastic jacket for protection 3 ½ inch, 1.44 MB
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Hard Disk Various sizes Portability Generally non-portable Removable hard disks available for PC Portable hard disk is gaining popularity Rigid platter coated with metallic substance
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Disk Pack Several platters Airtight, sealed module Mount disk pack on disk drive
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Logical Layout of a Disk Track Concentric circles Passes under read/write head as disk rotates 1.44 MB diskette has 80 tracks on each surface Each track stores the same amount of data
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Logical Layout of a Disk Sector Pie-shaped division of track Holds a fixed number of bytes (512 bytes) Cluster –Adjacent sectors treated as a unit of storage –Fixed number (2-8 sectors) –Minimum space allocated to a file
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Logical Layout of a Disk Zone Recording Assigns more sectors to tracks in outer zones More sectors = more data storage available
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Disk Drive Read / Write Operation Disks rotate Access arm moves read/write head Read / write operation begins and continues until complete Data is transferred to/from memory
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Optical Disk Greater capacity than other portable media Process Laser writes on metallic material spread over the surface of disk
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CD-ROM Compact Disk Read-Only Memory High capacity portable Read multiple times Cannot record Capacity – up to 680 MB (450 standard 3 ½ inch diskettes) Used for software distribution
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CD-R Compact Disc-Recordable High capacity Portable Write once Read multiple times CD-R drive CD-ROM drive
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CR-RW Compact Disk-Rewritable High capacity Portable Read multiple times Record multiple times Some compatibility problems reading CD- RW disks on CD-ROM drives
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DVD-ROM Digital Versatile Disk Larger capacity than CD-ROM Standard – Up to 4.7 GB, 7 times more than CD-ROM Double layers – 8.5 GB Double-sided – 17 GB Data is packed more densely Read multiple times, Cannot record Can read CD-ROM disks
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DVD-ROM Digital Versatile Disk Benefits Full-length movies Audio quality comparable to audio compact disks High-volume business data Expected to replace CD-ROM in the near future
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Blu-ray Disc Developed by the Blu- ray Disc Association (BDA) BDA includes company like Apple, Dell, Sony etc Developed to enable recording, rewriting and playback of high- definition video (HD)
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Blu-ray Disc DVD, DVD±R, DVD±RW, and DVD-RAM rely on a red laser Blu-ray use blue violate laser Benefits: Average disc holds 25GB/50GB. Advance BRD has storage capacity up to 500GB on a single disc by using 20 layers
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Magnetic Tape Storage Plastic tape with magnetic coating Magnetic tape unit Read/write head Erase head erases previously recorded data Inferior to disks Not as reliable Sequential access to data Inexpensive Primarily for backup
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Flash Drive USB flash drives are removable and rewritable reads and writes to flash memory. They are a solid-state storage medium that's both inexpensive and durable.
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Flash Drive (Contd.) Currently, USB 2.0 flash drives on the market are able to reach a data transfer speed of 480 Mbit/s and USB 3.0 has transmission speeds of up to 5 Gbit/s. More commonly used sizes vary from 2 Gigabytes -16 Gigabytes.
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