Storage Systems
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Transcript Storage Systems
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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