Discovering Computers 2008
Chapter 7
Storage
Access Time - Locate and Transfer data
Faster
Transfer
Rates
Primary Storage
Memory (RAM)
Stores
Items waiting to be interpreted and
executed by processor
Secondary Storage
Slower
Transfer
Rates
Hard Disk
Operating system, application
software, user data and information
CDs and DVDs
Software, backups, movies, music
Miniature Storage Media
Digital pictures or small files to be
transported
Tape
Floppy Disk
Backups
Small files to be transported
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 - 355 Fig. 7-1
Next
Storage

A storage device is the computer hardware that
records and/or retrieves items to and from storage
media
Reading is the process
of transferring items
from a storage medium
into memory
Writing is the process
of transferring items
from memory to a
storage medium
Page 354
4
Capacity
Number of Bytes Medium can Hold
NAME
AMOUNT
NUMBER
Kilobyte
1 Thousand
1,000
Megabyte
1 Million
1,000,000
Gigabyte
1 Billion
1,000,000,000
Terabyte
1 Trillion
1,000,000,000,000
Petabyte
1 Quadrillion
1,000,000,000,000,000
Exabyte
1 Quintillion
1,000,000,000,000,000,000
Zettabyte
1 Sextillion
1,000,000,000,000,000,000,000
Yottabyte
1 Septillion
1,000,000,000,000,000,000,000,000
MB = 700+ pages
GB = 262 ft of pages
TB = 51 miles of papers
PB = ¼ distance to moon
Petabyte: A Petabyte is approximately 1,000 Terabytes or one million Gigabytes.
It's hard to visualize what a Petabyte could hold. 1 Petabyte could hold approximately
20 million 4-drawer filing cabinets full of text. It could hold 500 billion pages of
standard printed text. It would take about 500 million floppy disks to store
the same amount of data.
Supercomputer hard disk=PB
Exabyte: An Exabyte is approximately 1,000 Petabytes. Another way to look at it is
that a Petabyte is approximately one quintillion bytes or one billion Gigabytes.
There is not much to compare an Exabyte to. It has been said that 5 Exabytes
would be equal to all of the words ever spoken by mankind.
Zettabyte: A Zettabyte is approximately 1,000 Exabytes. There is nothing to compare a
Zettabyte to but to say that it would take a whole lot of ones and zeroes to fill it up.
Yottabyte: A Yottabyte is approximately 1,000 Zettabytes. Again, there is nothing to
compare a Yottabyte with.
Capacity
Average Enterprise Storage Capacity
 412TB
San Diego Supercomputer Centre (SDSC) at the
University of California, San Diego,
36 PB as of 2/25/09
Largest Archival Storage Capacity of any
Educational Site
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
(USB, DVD’s ,
hard disks, CDs)
Contents
available to user
Contents
retained
Next
____ holds data, instructions, and information for
future use.
a. Storage
c. Throughput
b.
d.
Output
Input
______ storage is the physical material on which
a computer keeps data, instructions, and
information.
a. Primary
c. Tertiary
b. Secondary
d. all of the above
_______ is the number of bytes (characters) a
storage medium can hold.
a. Resolution
c. Capacity
b. Dimensionality
d. Retention
A(n) ____ device is the computer hardware that
records and/or retrieves items to and from
storage media.
a. concatenation c. resolved
b. indexed
d. storage
Disk References
A: — Always Primary Floppy Drive
B: — Secondary Floppy If It Exists
C: — Always Primary Hard Drive
D:, E:, F:, Etc. — Next Available Drive
 Hard drive
 CD-ROM
 DVD
 USB
 Network
Magnetic Media
Floppy Disk
 Original PC Storage
 Portable
Shutter
Shell
Liner
 Inexpensive
Magnetic
Coating
Metal Hub
Flexible Thin Film
Hard Disks

A hard disk contains one or more inflexible, circular
platters that use magnetic particles to store data,
instructions, and information
15
Magnetic Media
Formatting
 Preparing Disk for Reading & Writing
 Track

Circular Band on Disk Surface
 Sector

Pie-shaped

Bad Sectors
Marked as Unusable
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
FAT
Formatting prepares disk for use
p. 357 Fig. 7-5
Next
File Systems
FAT or FA T 16
• Support for hard drives up to 2 GB
• Cluster size was 32K – killed 64 sectors
• 8.3 file names
• VFAT -- 255 byte file names – Windows 95
FAT 32
• Support for hard drives up to 2 TB
• Cluster size is 4K to 16K - killed 8-32
sectors
NTFS
Cluster size is 4K to 16K
• Support for drives up to 256 TB
• More protection if system crashes
Clusters
4K for hard drives from 2GB to 16 TB
Magnetic Disks
http://www.youtube.com/watch?v=vjXU
5wXOXN8
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.
p. 360 Fig. 7-8
Head actuator positions
read/write head arms over
correct location on platters
to read or write data.
Next
Magnetic Media
Head Crash
 Spinning Creates Air Cushion

Floats Read / Write Head Above Platter
 Crash

Head Touches Platter Surface
 Clearance = Two-millionths of an Inch
Read/Write Head
Hair
Dust Smoke
Platter
Hard Disks –Cylinder Method of Storage
cylinder
What is a cylinder?
Location of a single track
through all platters
Single movement of
read/write head arms can
read same track on all
platters
track
Hard Disks

The hard disk arms
move the read/write
head, which reads
items and writes
items in the drive
 Location often is
referred to by its
cylinder
23
Magnetic Disks
What are characteristics of a hard disk?
Sample Hard Disk Characteristics
Advertised capacity
500 GB
Platters
4
Read/write heads
8
Cylinders
16,383
Bytes per sector
512
Sectors per track
63
Sectors per drive
973,773,168
Revolutions per minute
7,200
Transfer rate
300 MB per second
Access time
8.5 ms
p. 359 Fig. 7-7
actual
disk
capacity
Next
Operating System Utility Programs
What is a disk defragmenter?

Reorganizes files and unused space on hard
disk so programs run faster
p. 414 Fig. 8-19
Next
Magnetic Disks
What is a hard disk?
hard disk mounted
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
Click to view Web Link,
click Chapter 7, Click Web Link
from left navigation,
then click Perpendicular
Recording below Chapter 7
p. 358 Fig. 7-6
Perpendicular recording
Next
Perpendicular Storage
The storage industry currently makes hard drives using longitudinal
recording, which is reaching its physical limit. With this method, bits of data
are arranged horizontally on the recording magnetic medium.
Perpendicular recording methods arrange bits vertically so more can fit on, and
higher recording densities can be achieved without magnetic interference
which can corrupt data.
This method should mean hard drive storage based on moving mechanical parts
will be around for another 20 years or so, says Mr Pait.
http://news.bbc.co.uk/1/hi/technology/4080182.stm
Perpendicular Storage
http://www.hitachigst.com/hdd/research/recording_head/pr/
Click on Get Perpendicular
animation
Terabyte Living
Mr Pait thinks that …
in about five years PCs will have five terabytes of
storage on board.
2005
June 11,
One terabyte is the equivalent of 1,024GB
enough to hold more than 240,000 songs at the
standard encoding rate for digital music files.
Hard Disks
An external hard disk is a separate
free-standing hard disk that connects to
your computer with a cable or wirelessly
A removable hard disk is a hard disk
that you insert and remove from a drive
Internal and external hard disks are
available in miniature sizes (miniature
hard disks)
31
Magnetic Disks
What is a disk cache?

Don’t confuse
this cache with
portion of
memory that
processor uses
to store
frequently
accessed items
first request
for data—to disk cache
second request
for data—to hard disk
p. 361 Fig. 7-11
Memory cache on motherboard to RAM
(main memory on motherboard)
to disk cache on hard drive to
hard drive platters
More about caches
http://www.mackido.com/Hardware/Cache.html
The inflexible, circular platters on ____ disks use
magnetic particles to store data, instructions,
and information on a disk’s surface.
a.
hard
c.
optical
b.
digital
d.
indexed
The smallest unit of data a computer can process
is a(n) ____.
a. cluster
b. allocation
unit
c. bit
d. integer
____ is the process of dividing a disk into tracks
and sectors, so the operating system can store
and locate data and information on the disk.
a. Indexing
c. Recording
b. Formatting
d. Elongating
A(n) ____ is made of aluminum, glass, or
ceramic and is coated with an alloy material
that allows items to be recorded magnetically
on its surface.
a.
sector
c.
vector
b.
read/write
head
d.
platter
All of the following are characteristics of hard disks
EXCEPT ____.
a. write-protect notch c. sectors and tracks
b. read/write head
d. capacity
Some computers improve hard disk access time by
using a disk ____, which consists of memory chips
that store frequently accessed items.
a.
warehouse
c.
base
b.
cache
d.
home
Cloud Storage
Cloud storage is an Internet service that provides
storage to computer users
40
Cloud Storage
41
Cloud Storage
Users subscribe to cloud storage for a variety of reasons:
Access files from any computer
Store large files instantaneously
Allow others to access their files
View time-critical data and images immediately
Store offsite backups
Provide data center functions
42
Miniature Mobile Storage Media
What is a USB Flash Drive?




Plugs in a USB port on a
computer or mobile device
Storage capacities up to 64 GB
Has made the floppy disk
obsolete
May make hard drive obsolete
Moore’s Law ?????
Next
Kingston 256GB USB
This 256GB USB drive offers highest storage
capacity presently. (July - 26 – 2009)
Solid State Drives
Solid state media use flash memory chips and contain no
moving parts -- 640GB with 1.2TB (Moore’s Law)
Solid state drives (SSDs) have several advantages over
magnetic hard disks:
Faster access time
Faster transfer rates
Generate less heat and
consume less power
Last longer
45
Solid State Drives


Next Generation
http://www.youtube.com/watch?v=l4hbdZFWGog
Optical Discs
What are optical discs?

Push the button to
slide out the tray.
Flat, round, portable
metal discs made of
metal, plastic, and
lacquer

Can be read only or
read/write

Most PCs include an
optical disc drive
p. 366 Fig. 7-17
Insert the disc,
label side up.
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
Step 1.
Laser diode
shines a light
beam toward
disc.
p. 367 Fig. 7-18
laser
diode
lightsensing
diode
lens
land
Step 2.
If light strikes
a pit, it scatters.
If light strikes a
land, it is
reflected back
toward diode.
1
prism
laser
diode
lightsensing
diode
Step 3.
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
p. 367 Fig. 7-19
Next
Optical Discs
How should you care for an optical disc?
p. 368 Fig. 7-20
Next
Optical Discs
What is a CD-ROM?

Compact disc read-only memory
Same technology as audio CD’s

Cannot erase or modify contents

Typically holds 650 MB to 1 GB

Commonly used to distribute software and games
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
p. 369
Next
DVD Transfer Rates
DVD
Transfer Rate Transfer Rate Transfer Rate
Read/Write bytes/sec
KB/sec
MB/sec
Speed
1x
2x
3x
4x
5x
6x
8x
10x
12x
16x
1,385,000
2.770,000
4,155,000
5,540,000
6,925,000
8,310,000
11,080,000
13,850,000
16,620,000
22,160,000
1,352.54
2,705.08
4,057.62
5,410.16
6,762.70
8,115.23
10,820.31
13,525.39
16,230.47
21,640.63
http://www.osta.org/technology/dvdqa/dvdqa4.htm
1.32
2.64
3.96
5.28
6.60
7.93
10.57
13.21
15.85
21.13
Equivalent CDR/CD-RW
read/ write speed
9x
18x
27x
36x
45x
54x
-----
Optical Discs
DVD Formats Explained
A CD-ROM can be read from but not
written to
• Read from a CD-ROM drive or CD-ROM player
A CD-R is a multisession optical disc on
which users can write, but not erase
A CD-RW is an erasable multisession disc
• Must have a CD-RW drive
54
Optical Discs
Junk Closet
A DVD-ROM is a high-capacity optical
disc on which users can read but not
write or erase
• Requires a DVD-ROM drive
A Blu-ray Disc-ROM (BD-ROM) has a
storage capacity of 100 GB
DVD-RW, DVD+RW, and DVD+RAM
are high-capacity rewritable DVD
formats -- Hybrid (DVD±RW) drives
55
How should you care for a
DVD?
U:\WEBSITE\PEOPLE\FACULTY\zlotow\PP Slides\DVDCare.htm
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
p. 372 - 373 Fig. 7-25
Next
Other Types of Storage
61
Tape
What is tape?
 Magnetically coated plastic ribbon
capable of storing large amounts
of data at low cost
 Primarily used for backup
Web site for tape drives
p. 374 Fig. 7-27
Next
Tape
How is data stored on a tape?
 Sequential access

Reads and writes data consecutively — used for music
tapes or VHS
 Direct access

p. 374
Locates a file immediately— used for hard disks, CDs,
and DVDs
Next
Microfilm and Microfiche
What are microfilm and microfiche?
Store microscopic images of
documents on roll or sheet of
film
Microfilm — 100- to
215-foot roll of film
Microfiche — small sheet
of film, usually 4”  6”
p. 379 Fig. 7-34
Next
Microfilm and Microfiche
Who uses microfilm and microfiche?
1. Libraries for back issues
2. Banks for cancelled checks
3. Archival of inactive files
4. US Army for personnel records
What are the advantages of microfilm
and microfiche?
1. Reduce amount of paperwork
2. Inexpensive
3. Longest life of any storage media
Next
Microfilm and Microfiche
How do life expectancies of various media compare?

Microfilm and microfiche have longest life of any storage media
p. 379 Fig. 7-35
Next