Storage and Multimedia: The Facts and More

Chapter 6

Secondary Storage Device

Secondary Storage Benefits

Semi-permanent Non-volatileReliableConvenient – 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 StorageData represented as magnetic spots

Magnetized spot = 1 Absence of a magnetized spot = 0

Read Converts the magnetized data to

electrical impulsesWrite

Converts electrical impulses to magnetized spots on disk

Diskettes

Low capacity – small files

PortableFlexible Mylar coated

with metallic substanceHard plastic jacket for

protection3 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 plattersAirtight, sealed module

Mount disk pack on disk drive

Logical Layout of a DiskTrack

Concentric circlesPasses under read/write head as disk

rotates1.44 MB diskette has 80 tracks on each

surfaceEach track stores the same amount of

data

Logical Layout of a DiskSector

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 DiskZone Recording

• Assigns more sectors to tracks in outer zones

• More sectors = more data storage available

Disk DriveRead / 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 DiskGreater capacity

than other portable media

Process Laser writes on

metallic material spread over the surface of disk

CD-ROMCompact Disk Read-Only Memory

High capacity portableRead multiple timesCannot recordCapacity – up to 680 MB (450

standard 3 ½ inch diskettes)Used for software

distribution

CD-RCompact Disc-Recordable

High capacityPortableWrite onceRead multiple times

CD-R drive CD-ROM drive

CR-RWCompact Disk-Rewritable

High capacityPortableRead multiple timesRecord multiple timesSome compatibility problems reading

CD-RW disks on CD-ROM drives

DVD-ROMDigital 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 denselyRead multiple times, Cannot recordCan read CD-ROM disks

DVD-ROMDigital 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.