Storage and Multimedia: The Facts and More Chapter 6

Secondary Storage Device

Secondary Storage Benefits  Semi-permanent  Non-volatile  Reliable  Convenient – Locate and access data quickly

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

Types of Storage  Magnetic Disk Storage  Optical Disks  CD-ROM  CD-R  CD-RW  DVD-ROM  Blu-ray  Magnetic Tape Storage  Flash Drive

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

Diskettes  Low capacity – small files  Portable  Flexible Mylar coated with metallic substance  Hard plastic jacket for protection  3 ½ inch, 1.44 MB

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

Disk Pack Several platters Airtight, sealed module Mount disk pack on disk drive

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

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

Logical Layout of a Disk Zone Recording Assigns more sectors to tracks in outer zones More sectors = more data storage available

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

Optical Disk  Greater capacity than other portable media  Process  Laser writes on metallic material spread over the surface of disk

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

CD-R Compact Disc-Recordable  High capacity  Portable  Write once  Read multiple times  CD-R drive  CD-ROM drive

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

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

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

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)

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

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

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.

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.