Intro to Info Tech
Storage Devices
This presentation can be viewed on line at:
http://web.fscj.edu/Janson/cgs1060/wk08.Storage.ppt
Copyright 2003
by Janson Industries
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Objectives


Explain the various devices
Explain and compare the
relative advantages and
disadvantages
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Storage Devices


Hold data and instructions, can
also hold output
Comprised of a device and media
 Device
writes to and reads from a
particular medium


Been around since beginning of
computers
Early medium – punch cards
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Storage Devices

Measured two ways
 Speed
(access/write/rewrite)
 Capacity

Also, compared according to
– can medium be
moved to another device
 Portability
– once written to
can medium be it be changed
 "Rewritability"
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Storage Devices

Secondary storage vs. Internal
storage (Main Memory/MM)
 Slower
access
 SS
measured in microseconds, PC
MM nanoseconds
 Holds
 PC
much more
MM measured in GB, SS TB
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Storage Device Types

Magnetic Disks

Optical Disks

Other
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Magnetic Disks

Surface can be magnetized and
demagnetized
 Magnetic

state represents a 0 or 1
Surface broken up into
 Tracks
 Pie
shaped sections
 Sectors
 Tracks
and sections numbered
 This provides identifier for sectors
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Magnetic Disks

2 types
 Floppy
disk/floppy drive
 Portable
 Hard
media
disk/hard drive
 Some
are/some are not portable
 Most desktop PCs have a single unit
where medium can't be separated
and moved to another device
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Floppy Disks

Historically, different sizes
 3.5,
 3.5
5.25, 8
holds about 1.44 megs

Single vs. double sided

Zip disks hold a lot more
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Hard Disk


Made up of multiple inflexible
platters
Read/write heads
 One

for each platter surface
How heads and platter work:
 Heads
2 millionths of an inch over
surface
 Sense the magnetic state of
platter surface
 Head crash – Bad!
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Hard Disk

How the whole thing works
 Arm
extended to correct track
 Platter
spun so correct sector is
under read/write head
 Surface
read and value sent via
circuitry through the arm

http://www.youtube.com/watch?v=9
eMWG3fwiEU
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Hard Disk

With hard disks, different units of
storage
 Cluster:
group of adjacent sectors,
smallest unit of allocatable storage
 Cylinder: all same tracks on different
platter surfaces

To make access faster try to store
info
 In
one track
 If data larger than a track, store in
same cylinder
 Why?
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Other Hard Disks

External hard disks
 One
unit separate from system unit
 Plugs into USB port
 Capacity in TBs
 Some more portable than others

Removable HD
 Very
portable
 Machines must have a removable
HD bay
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Other Hard Disks

Miniature HDs
 Often
built into a mobile device like
camera, headphones
 Pocket HD has more capacity than a
thumb

Large systems have many hard
drives
 Will
have disk controller(s)
 Specialized
chip that manages
communication with disk drives
 Decreases work for the CPU
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Optical Disks



Surface of the disk is altered to
affect it's reflectivity
To read, a beam of light is shot
onto the surface
The amount of light reflected will
represent a 0 or 1
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Optical Disks

Compared by their
 Sidedness
 Capacity
 Speed
 Read/Write
capability
 Reading
is called ripping
 Writing is called burning

2 major types
 CDs
 DVDs
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Compact Discs

Usually
 One
sided
 Capacity

650MB – 1GB
Different types determined by the
read/write capability
 CD-ROM
 CD-R
 CD-RW
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Compact Discs

CD-ROM (Read Only Memory)
 Single
 Can
read many times
 Used

session – can write to disc once
to be called a WORM disc
What good is this type of CD?
 S/W
mfgs write to these type of disks
and then distribute
 Users
can't inadvertently erase the
application
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Compact Discs

CD-R (Read)
– can write to one portion
of disk and then later to another
 Multi-session
 Can
read many times
 Can't

erase what is written
CD-RW (Rewritable)
 Can
write, read, erase, and rewrite to
disc
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CD Drives

Compared by
 The
type of discs they support
 Can
 Read,
they read and/or write
write, rewrite speed
 Measured
like this:
 Read
128X
 Write 64X
 Rewrite 24X
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DVDs

Digital Versatile Disc
 Holds
more than CDs
 4.7GB
to 100GB
 Capacity
depends on whether
 Single
or double sided
 Regular or high capacity DVD
 Single or multiple layers
 Battle
for high capacity DVD format
between Blu-ray and HD
 Blu-ray
won! (BD)
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Reading and Writing to DVDs

For Blu-ray, two types of discs
 BD-R
is read only
 BD-RE can read and write

Regular discs are more complicated
 DVD+R
and DVD-R are read only
 DVD+RW, DVD-RW, and DVD+RAM
can read and write

The DVD drive must support the
particular DVD format
 Most
DVD drives support CDs
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Reading and Writing to DVDs

DVD-R approved by DVD Forum
 Mitsubishi,

DVD+R supported by the DVD+RW
Alliance.
 Sony,

Sony, Hitachi, and Time Warner
Yamaha, Philips, Dell, and HP
Differences
 Defects
management
 How DVDs are formatted and rewritten
 What TV DVD players will play them
 For computer backups, either one will do
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Other Storage

Tape
A
magnetic ribbon
 Two
formats:
 Cartridge
 Reel
 Only
to reel
provides sequential access
 Discs
 Tapes
provide direct access
often used for back up
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Other Storage


Flash memory cards
 Flash
memory (i.e. chip based)
 Used
in notebooks, cameras, PDAs
 Need
a special drive/slot in device
USB Flash drives (aka Thumb drives)
 Comprised
of both media and device
 Don't
need special drive/slot, just
need a USB port
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Other Storage

Smart cards
 Chip
based memory
 Can
also process information
 Holds
a defined amount of money
 You buy something, that amount is
decreased

Online
 Can
access files from anywhere
 Give
others access
 Many
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are free
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Online Storage

Three big players (as of 5/2012)
 Google
5
Drive
GB free, 100GB more $59.88
 OneDrive
 15
GB free (7/14), 100GB more $50.00
 Dropbox
2
-formerly Skydrive (MS)
(Dropbox Inc.)
GB free, 100GB more $199.00
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Online Storage

Also compared based on
 Search
– can file content be basis
 Dropbox
only scans file names
 OneDrive
supports content scan for MS
formats (Word, Excel, PP, etc.)
 Google
supports many formats, even uses
OCR for scanned content
 Others
 With
access
Google Drive, file is either view or edit
 OneDrive
 Dropbox
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lets you specify for each file/user
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must set up a shared folder for edit
Other Storage

Microfilm and Microfiche
 Film
is reel to reel, fiche is small rectangle
of plastic film
 Hold microscopic images
 Need separate devices to read and write
 Readers considered auxiliary devices not
peripheral devices
 Don't
need the CPU to access the storage
medium
 Extremely
long lasting 100-500 years
 Magnetic
disk 5-30 yrs
 Optical 10-100 yrs
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Other Storage


Enterprise storage - vast
amount of capacity
Storage array
 Separate
device comprised of
hundreds of disks
 Have multiple processors
 Act as "storage servers"
 Capacities up to .5 PB (half a
quadrillion bytes)
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Other Storage

Solid state hard drive (SSD)
 Uses
non-volatile memory chips
 No moving parts
 Much faster than magnetic disk (up
to 100X)
 More expensive (up to 20X)
 Limited number of writes (1-5 mill)

Often used in combination with
magnetic disk
 SSD
acts as cache for frequently
used files
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Points to Remember



Secondary storage: non-volatile
storage managed by a dedicated
storage device
Secondary storage serves as a
source of input and target for output
Wide variety of media measured by
 Speed
 Capacity
 Durability
 Read/write
capability
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