IT_Chapter_6A

Describing Storage Devices

• Store data when computer is off

• Two processes

– Writing data

– Reading data

• Storage terms

– Media is the material storing data

– Storage devices manage the media

– Magnetic devices use a magnet

– Optical devices use lasers

– Solid-state devices have physical switches

Magnetic Storage Devices

• Most common form of storage

• Hard drives, floppy drives, tape

• All magnetic drives work the same

• Data storage and retrieval

– Media is covered with iron oxide

– Read/write head is a magnet

– Magnet writes charges on the media

• Positive charge is a 1

• Negative charge is a 0

– Magnet reads charges

– Drive converts charges into binary

• Data organization

– Disks must be formatted before use

– Format draws tracks on the disk

– Tracks is divided into sectors

• Amount of data a drive can read

• Finding data on disk

– Each track and sector is labeled

• Some are reserved

– Listing of where files are stored

• File Allocation Table (FAT)

• FAT32

• NTFS

– Data is organized in clusters

• Size of data the OS handles

• Diskettes

– Also known as floppy disks

– Read with a disk drive

– Mylar disk

– Spin at 300 RPM

– Takes .2 second to find data

– 3 ½ floppy disk holds 1.44 MB

• Hard disks

– Primary storage device in a computer

– 2 or more aluminum platters

– Each platter has 2 sides

– Spin between 5,400 to 15,000 RPM

– Data found in 9.5 ms or less

– Drive capacity greater than 40 GB

• Removable high capacity disks

– Speed of hard disk

– Portability of floppy disk

– Several variants have emerged

– High capacity floppy disk

• Stores up to 750 MB of data

– Hot swappable hard disks

• Provide GB of data

• Connect via USB

• Tape drives

– Best used for

• Infrequently accessed data

• Back-up solutions

– Slow sequential access

– Capacity exceeds 200 GB

Optical Storage Devices

• CD-ROM

– Most software ships on a CD

– Read using a laser

• Lands, binary 1, reflect data

• Pits scatter data

– Written from the inside out

– CD speed is based on the original

• Original CD read 150 Kbps

• A 10 X will read 1,500 Kbps

– Standard CD holds 650 MB

• DVD-ROM

– Digital Video Disk

– Use both sides of the disk

– Capacities can reach 18 GB

– DVD players can read CDs

Recordable Optical Technologies

• CD Recordable (CD-R)

– Create a data or audio CD

– Data cannot be changed

– Can continue adding until full

Recordable Optical Technologies

• CD Regrettable (CD-RW)

– Create a reusable CD

– Cannot be read in all CD players

– Can reuse about 100 times

Recordable Optical Technologies

• Photo CD

– Developed by Kodak

– Provides for photo storage

– Photos added to CD until full

– Original pictures cannot be changed

Recordable Optical Technologies

• DVD Recordable

– Several different formats exist

– None are standardized

– Allows home users to create DVDs

– Cannot be read in all players

Recordable Optical Technologies

• DVD-RAM

– Allow reusing of DVD media

– Not standardized

– Cannot be read in all players

Solid State Devices

• Data is stored physically

• No magnets or laser

• Very fast

• Flash memory

– Found in cameras and USB drives

– Combination of RAM and ROM

– Long term updateable storage

• Smart cards

– Credit cards with a chip

– Chip stores data

– Eventually may be used for cash

– Hotels use for electronic keys

• Solid-state disks

– Large amount of SDRAM

– Extremely fast

– Volatile storage

– Require battery backups

– Most have hard disks copying data