Chapter 7Storage

StorageWhat is storage?

p. 348 Fig. 7-1 Next

Holds data, instructions, and information for future use

Storage medium is physical material used for storage

Also called secondary storage

StorageWhat is capacity?

p. 350 Next

Kilobyte (KB) 1 thousand

Megabyte (MB) 1 million

Gigabyte (GB) 1 billion

Terabyte (TB) 1 trillion

Petabyte (PB) 1 quadrillion

Number of bytes (characters) a storage medium can hold

Exabyte (EB) 1 quintillion

Zettabyte (ZB) 1 sextillion

Yottabyte (YB) 1 septillion

Storage Medium(floppy disks, Zip disks,

hard disks, CDs)

StorageHow does volatility compare?

p. 350 Next

No

nvo

lati

le

Storage medium is nonvolatile—contents retained when power is off

Contents Contents retainedretained

Contents available Contents available to userto user

Memory(most RAM)

(chips on motherboard)

Screen Display

ON OFF

Vo

lati

le Display Display disappearsdisappears

Data andData andinstructions instructions

available to useravailable to user

Display Display appearsappears

Data and instructions Data and instructions erasederased

Memory is volatile—holds data and instructions temporarily

WritingWriting

Process of transferring Process of transferring items from memory items from memory

to storage mediato storage media

WritingWriting

Process of transferring Process of transferring items from memory items from memory

to storage mediato storage media

StorageWhat is a storage device?

p. 350 Next

ReadingReading

Process of transferring Process of transferring items from storage items from storage media to memorymedia to memory

ReadingReading

Process of transferring Process of transferring items from storage items from storage media to memorymedia to memory

Hardware that Hardware that records and records and

retrieves items retrieves items to and from to and from

storage mediastorage media

Functions as source of input

Creates output

Floppy Disk Small files to be transported

Secondary Storage

Primary Storage

Hard Disk

CDs and DVDs

Miniature Storage Media

Tape

Items waiting to be interpretedand executed by the processor

Operating system, applicationsoftware, user data and informationSoftware, backups, movies, music

Digital pictures or small files tobe transported

Backups

Memory (most RAM)

Stores …

StorageWhat is access time?

p. 350

Time it takes storage device to locate item on storage medium

Next

Time required to deliver item from memory to processor

fastertransfer

rates

slowertransfer

rates

Floppy DisksWhat is a floppy disk?

p. 351 Fig. 7-5 Next

Portable, inexpensive storage medium (also called diskette)

Thin, circular, flexible film enclosedin 3.5” wide plastic shell

shutter

shell

liner

magneticcoating

flexible thin film

metal hub

Floppy DisksWhat is a floppy disk drive?

p. 352 Fig. 7-6 Next

Floppy disk drive built intoa desktop computer

External floppy disk drive attaches toa computer with a cable

Also called secondary storage

One floppy drive, named drive A If two floppy drives, second

designated as drive B

Device that reads from andwrites to floppy disk

Floppy Disks

p. 353 Fig. 7-8 Next

What are tracks and sectors?

Trackis narrow

recording bandthat forms fullcircle on disk

Sector stores up to512 bytes

of data

Formatting prepares disk for use and marks bad sectors as unusableClick to view Web Link,click Chapter 7, Click Web Linkfrom left navigation, then click Floppy Disks below Chapter 7

Floppy DisksHow do you compute a disk’s storage capacity?

p. 354 Fig. 7-9 Next

Multiply number of sides, number of tracks, number of sectors per track, and number of bytes per sector For high-density disk: 2 sides 80 tracks 18 sectors per track 512

bytes per sector = 1,474,560 bytes

Characteristics of a3.5-inch High-DensityFloppy Disk

Capacity: 1.44 MB

Sides: 2

Tracks: 80

Sectors per track: 512

Sectors per disk: 2880

Floppy DisksWhat is a write-protect notch?

p. 354 Fig. 7-10 Next

Small opening with a cover that you slide Protects floppy disk from being erased accidentally

hole on thisside meansdisk is high

density

hole on thisside meansdisk is high

density

write-protected

not write-protected

notch closedmeans you

can write onthe disk

notch closedmeans you

can write onthe disk

notch openmeans you

cannot writeon the disk

notch openmeans you

cannot writeon the disk

ExternalZip drive

Zip® DisksWhat is a Zip disk?

p. 355 Fig. 7-11 Next

Magnetic medium that stores 100 MB to 750 MB of data

Zip disks require a Zip drivec—chigh capacity drive that reads from and writes on a Zip disk

Used to back up and to transfer files

Backup is duplicate of file, program, or disk in case original is lost

c

Zip disk

Click to view Web Link,click Chapter 7, Click Web Linkfrom left navigation, then click Zip Disksbelow Chapter 7

Hard DisksWhat is a hard disk?

p. 355 Fig. 7-12 Next

hard disk installedin system unit

High-capacity storage Consists of several inflexible,

circular platters that store items electronically

Components enclosed in airtight, sealed case for protection

Click to view Web Link,click Chapter 7, Click Web Linkfrom left navigation, then click Hard Disk below Chapter 7

Hard DisksWhat are characteristics of a hard disk?

p. 356 Fig. 7-13 Next

Sample Hard Disk Characteristics

Advertised capacity 120 GBPlatters 3Read/write heads 6Cylinders 16,383Bytes per second 512Sectors per track 63Sectors per drive 234,441,648Revolutions per minute 7,200Transfer rate 133 MB per secondAccess time 8.9 ms

actualdisk

capacity

Hard DisksHow does a hard disk work?

p. 357 Fig. 7-14 Next

Step 1.Circuit board controls movement of head actuator and a small motor.

Step 2.Small motor spins platters while computer is running.

Step 3.When software requests a disk access, read/write heads determine current or new location of data.

Step 4.Head actuator positions read/write head arms over correct location on platters to read or write data.

Hard DisksWhat is a cylinder?

p. 357 Fig. 7-15 Next

Vertical section of track through all platters

Single movement of read/write head arms accesses all plattersin cylinder

platter

read/writehead

platter

sides

cylinder

track

sector

Click to view animation