LECTURE 5: STORAGE
LECTURE 5: STORAGE
Chapter 5 Objectives
Differentiate between storage devices
and storage media
Describe the characteristics of
magnetic disks
Differentiate among CD-ROMs,
recordable CDs, rewritable CDs,
DVD-ROMs, recordable DVDs, and
rewritable DVDs
Describe the characteristics of
a hard disk
Identify the uses of tape
Differentiate between floppy disks
and Zip disks
Discuss PC Cards and the various types
of miniature mobile storage media
Describe the characteristics
of optical discs
Identify uses of microfilm and
microfiche
Storage
What is storage?
Holds data, instructions, and information for future use
Storage medium is physical material used for storage
Also called secondary storage
p. 354 Fig. 7-1
Next
Storage
What is capacity?
Number of bytes (characters) a storage medium can hold
Kilobyte (KB)
1 thousand
Megabyte (MB) 1 million
p. 356
Gigabyte (GB)
1 billion
Terabyte (TB)
1 trillion
Petabyte (PB)
1 quadrillion
Exabyte (EB)
1 quintillion
Zettabyte (ZB)
1 sextillion
Yottabyte (YB)
1 septillion
Next
Storage
How does volatility compare?
Nonvolatile
Volatile
Storage medium is nonvolatile—contents retained when
power is off
Memory is volatile—holds data and instructions temporarily
p. 356
ON
OFF
Screen Display
Display
appears
Display
disappears
Memory
(most RAM)
(chips on motherboard)
Data and
instructions
available to user
Data and
instructions erased
Storage Medium
(floppy disks, Zip disks,
hard disks, CDs)
Contents
available to user
Contents
retained
Next
Storage
What is a storage device?
Reading
Process of transferring
items from storage
media to memory
Hardware that
records and
retrieves items
to and from
storage media
Functions as source
of input
p. 356
Writing
Process of transferring
items from memory
to storage media
Creates output
Next
Storage
What is access time?
Time it takes storage device to locate item on storage medium
Time required to deliver item from memory to processor
faster
transfer
rates
Transfer rates
Stores …
Primary Storage
Memory (most RAM)
Items waiting to be interpreted
and executed by the processor
Secondary Storage
Hard Disk
Flash Memory Cards
and USB Flash Drives
CDs and DVDs
slower
transfer
rates
Tape
Floppy Disk
Operating system, application
software, user data and information
Digital pictures or files
to be transported
Software, backups, movies, music
Backups
Small files to be transported
Next
Magnetic Disks
What are tracks and sectors?
Track
is narrow
recording band
that forms full
circle on disk
Sector
stores up to
512 bytes
of data
Formatting prepares disk for use and marks bad sectors as unusable
Next
Magnetic Disks
What is a hard disk?
hard disk installed
in system unit
High-capacity storage
Consists of several
inflexible, circular
platters that store items
electronically
Components enclosed in
airtight, sealed case for
protection
Longitudinal recording
Perpendicular recording
Next
Magnetic Disks
What are characteristics of a hard disk?
Sample Hard Disk Characteristics
Advertised capacity
Platters
Read/write heads
Cylinders
Bytes per second
Sectors per track
Sectors per drive
Revolutions per minute
Transfer rate
Access time
120 GB
3
6
16,383
512
63
234,441,648
7,200
133 MB per second
8.9 ms
actual
disk
capacity
Next
Magnetic Disks
How does a hard disk work?
Step 3.
Step 2.
When software requests a
disk access, read/write
heads determine current
or new location of data.
Small motor spins
platters while
computer is running.
Step 4.
Step 1.
Circuit board controls
movement of head actuator
and a small motor.
Head actuator positions
read/write head arms over
correct location on platters
to read or write data.
Next
Magnetic Disks
platter
What is a cylinder?
Vertical section of
track through all
platters
Single movement
of read/write head
arms accesses all
platters
in cylinder
track
sector
read/write
head
platter
sides
cylinder
Next
Magnetic Disks
A magnetic hard disk
consists of either a
single rigid platter or
several platters that
spin together on a
common spindle. A
movable access arm
positions the read and
write mechanisms over,
but not quite touching,
the recordable surfaces.
Magnetic Disks
What is a head crash?
Occurs when read/write head touches platter surface
Spinning creates cushion of air that floats read/write head above platter
Clearance between head and platter is approximately two-millionths of an inch
A smoke particle, dust particle, or human hair could render drive unusable
hair
read/write head
dust
smoke
clearance
platter
Next
GMR, hard disc and Nobel Prize
Giant magnetoresistance
(GMR) is a quantum
mechanical magnetoresistance
effect observed in thin film
structures composed of
alternating ferromagnetic and
nonmagnetic layers.
2007 Nobel Prize
Magnetic head
Magnetic Disks
What is a disk cache?
Portion of
memory that
processor uses
to store
frequently
accessed items
processor
disk cache
first request
for data—to disk cache
second request
for data—to hard disk
hard disk
Next
Magnetic Disks
What are external hard disks and removable hard disks?
Used to back up or transfer files
Removable hard disk—hard disk
that you insert and remove
from hard disk drive
External hard disk—freestanding
hard disk that connects to system unit
Next
Magnetic Disks
What is a disk controller?
Chip and circuits that
control transfer of
items from disk
SATA (Serial
Serial Advanced
Technology Attachment)
Attachment) controller
uses serial signals to transfer data,
instructions, and information
SCSI
EIDE (E
Enhanced Integrated Drive (Small Computer System Interface)
controller supports up to fifteen
Electronics) controller supports four
devices including hard disks, CD
hard disks, provides connections for
and DVD drives, tape drives, printers,
CD and DVD drives
scanners, network cards
Next
Magnetic Disks
What is online storage?
Service on Web that provides storage for
minimal monthly fee
Files can be accessed from
any computer with Web
access
Large files can be downloaded
instantaneously
Others can be authorized
to access your data
Next
Magnetic Disks
What is a floppy disk?
shutter
Portable, inexpensive storage
medium (also called diskette)
shell
liner
magnetic
coating
Thin, circular, flexible film enclosed
in 3.5” wide plastic shell
metal hub
flexible thin film
Next
Magnetic Disks
What is a floppy disk drive?
Device that reads from and
writes to floppy disk
One floppy drive, named drive A
Also called secondary storage
External floppy disk drive
attaches to a computer with
a cable
Floppy disk drive built into
a desktop computer
Next
Magnetic Disks
What is a write-protect notch?
Small opening with a cover that you slide
Protects floppy disk from being erased accidentally
write-protected
notch open
means you
cannot write
on the disk
notch closed
means you
can write on
the disk
not write-protected
hole on this
side means
disk is high
density
Next
Magnetic Disks
How do you compute a disk’s storage capacity?
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
Capacity:
Characteristics of a
3.5-inch High-Density
Floppy Disk
1.44 MB
Sides:
2
Tracks:
80
Sectors per track:
18
Bytes per sector:
512
Sectors per disk:
2880
Next
Optical Discs
What are optical discs?
Flat, round, portable
metal discs made of
metal, plastic, and
lacquer
Can be read only or
read/write
Push the button to
slide out the tray.
Insert the disc,
label side up.
Most PCs include an
optical disc drive
Push the same button
to close the tray.
Next
Optical Discs
How does a laser read data on an optical disc?
disc label
lens
pit
0
prism
lightsensing
diode
Step 1.
Laser diode
shines a light
beam toward
disc.
laser
diode
lens
land
Step 3.
Step 2.
If light strikes
a pit, it scatters.
If light strikes a
land, it is
reflected back
toward diode.
1
prism
lightsensing
diode
laser
diode
Reflected light is
deflected to a
light-sensing diode,
which sends digital
signals of 1 to
computer. Absence
of reflected light is
read as digital
signal of 0.
Next
Optical Discs
How is data stored on an optical disc?
Typically stored in
single track
Track divided
into evenly
sized sectors
that store
items
single track
spirals to edge
of disc
disc sectors
Next
Optical Discs
How should you care for an optical disc?
Do not
eat, smoke, or
drink near
a disc
Do not expose
the disc to
excessive
heat or
sunlight
Do not stack discs
Do not touch
the underside
of the disc
Do store the
disc in a jewel
box when
not in use
Do hold a disc
by its edges
Next
Optical Discs
What is a CD-ROM?
Compact disc read-only memory
Cannot erase or modify contents
Typically holds 650 MB to 1 GB
Commonly used to distribute multimedia and complex software
Next
Optical Discs
What is the data transfer rate of a CD-ROM drive?
Ranges from
48X to 75X
or faster
75X is 150 KBps
(KB per second)
75X
75 × 150 KBps = 11,250 KBps
or 12.25 MBps
48X:
48 × 150 KBps = 7,200 KBps
or 7.2 MBps
Next
Optical Discs
What are CD-Rs and CD-RWs?
Must have
CD recorder
or CD-R drive
CD-R (compact disc-recordable)
— disc you can write on once
c
Cannot erase
disc’s contents
CD-RW (compact disc-rewritable)
— erasable disc you can write on
multiple times
ce
Must have
CD-RW software
and CD-RW drive
Next
Optical Discs
What is a DVD-ROM (digital versatile
disc-ROM or digital video disc-ROM)?
Must have DVD-ROM drive or
DVD player to read DVD-ROM
Stores databases, music,
complex software, and movies
Blu-ray discs have storage
capacity of up to 27 GB
HD-DVD discs have storage
capacity of up to 45 GB
UMD can store up to 1.8 GB
Next
Optical Discs
How does a DVD-ROM store data?
Two layers of pits are used, lower layer is
semitransparent so laser can read through
Some are double-sided
Many types of recordable and rewritable DVDs are
available
DVD-R and DVD+R
DVD-RW and DVD+RW
Next
Tape
What is tape?
Magnetically coated plastic ribbon
capable of storing large amounts
of data at low cost
Primarily used for backup
Next
Tape
How is data stored on a tape?
Sequential access
Reads and writes data consecutively, like music tape
Unlike direct access — used on floppy disks, Zip disks,
hard disks, CDs, and DVDs — which can locate
particular item immediately
Next
Miniature Mobile Storage Media
What are common types of flash memory cards?
CompactFlash
Smart Media
Memory Stick
Secure Digital
xD Picture Card
Next
Miniature Mobile Storage Media
How does one type of flash memory card work?
Next
Miniature Mobile Storage Media
What is a USB Flash Drive?
Plugs in a USB port on a
computer or mobile device
Storage capacities from 1G up
to ? GB
May eventually make the
floppy disk obsolete
Next
Microfilm and Microfiche
What are microfilm and microfiche?
Store microscopic images of
documents on roll or sheet of
film
Images recorded using
computer output microfilm
recorder
Microfilm — 100- to
215-foot roll of film
Microfiche — small sheet
of film, usually 4” × 6”
Next
Microfilm and Microfiche
How do life expectancies of various media compare?
Microfilm and microfiche have longest life of any storage media
Next
Putting It All Together
What are recommended storage devices for home
users?
160 GB hard disk
Online storage
CD or DVD drive
Card reader/writer
USB flash drive
Next
Putting It All Together
What are recommended storage devices for small
office/home office (SOHO) users?
250 GB hard disk
Online storage
CD or DVD drive
External hard drive for backup
USB flash drive
Next
Putting It All Together
What are recommended storage devices for mobile
users?
100 GB hard disk
Online storage
CD or DVD drive
Card reader/writer
Portable hard disk for backup
USB flash drive, and/or 5 GB PC Card hard
disk
Next
Putting It All Together
What are recommended storage devices for power
users?
CD or DVD drive
500 GB hard disk
Online storage
Portable hard disk for backup
USB flash drive
Next
Putting It All Together
What are recommended storage devices for large
business users?
Desktop computer
250 GB hard disk
CD or DVD drive
Smart card reader
Tape drive
USB flash drive
Server or Mainframe
Network storage server
40 TB hard disk system
CD-ROM or DVD-ROM server
Microfilm or microfiche
Next
Summary of Storage
Internal hard disks
Recordable DVDs
Portable hard disks
Rewritable DVDs
Floppy disks
Tape
Zip disks
PC Cards
CD-ROMs
Recordable and Rewritable CDs
DVD-ROMs
Flash memory cards and
USB flash drives
Smart cards, microfilm, and
microfiche
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