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Types of Storage
LECTURE 6
• Storage refers to the media used to store data and
software in a permanent form.
• Contrary to memory (RAM), information in storage
does not disappear when the computer is turned off.
• Several different types of technology and media are
used for storage:
Storage of data and
programs in a computer
–
–
–
–
–
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Relationship between speed and cost of
various memory and storage options
Cost / byte
Faster and smaller
components are
usually more
expensive.
2
ƒ The next big advance over paper was magnetic tape
Primary disadvantage - must be read linearly
L2
L2 cache
cache
ƒ The key technological breakthrough that enabled
the creation of the hard disk came in the 1950s
SDRAM
SDRAM
Hard
Hard Disk
Disk
CD
CD Drive
Drive
ƒ Heads were suspended above the surface of the disk
and could read the bits as they passed underneath.
Floppy
Floppy Disk
Disk
Speed
Tape
Tape Drive
Drive
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ƒ The first storage medium was paper
L3
L3 cache
cache
Storage
Storage
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Earliest computers had no storage
CPU
CPU register
register
L1
L1 cache
cache
Memory
Memory
Paper tapes, cards (historical)
Magnetic tape, disks, diskettes
Optical
Magneto-optical
PC cards, flash cards, SD cards, CF cards
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Hard disks and cassette tapes
Magnetic Memory
Hard disks and cassette tapes use the same
magnetic recording techniques
Magnetic core memory
was popular main
memory for computers
through the 1960s until it
was completely replaced
by semiconductor
memory.
ƒ Share the major benefits of magnetic storage.
ƒ Can be easily erased and rewritten and will "remember"
the magnetic flux patterns stored for many years.
ƒ With a tape, fast-forward or reverse can be used to get to any
particular point. In a cassette-tape deck, the read/write head
touches the tape directly. The tape moves at about 2 inches/sec.
ƒ The hard-disk platter spins at speeds up to 3,000 inches per
second (about 170 mph).
ƒ Information on a hard disk is stored in extremely small magnetic
domains compared to a cassette tape.
These were actually little circular magnets
that were strung on intersecting wires
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1
Evolution of the hard disk
History of the Hard Disk
First Hard Disk (1956): IBM's RAMAC is introduced. It has a capacity of about 5 MB,
stored on 50 24" disks.
First Air Bearing Heads (1962): IBM's model 1301 lowers the flying height of the heads to
250 microinches. It has a 28 MB capacity on half as many heads as the original RAMAC,
and increases both areal density and throughput by about 1000%.
First Modern Hard Disk Design (1973): IBM's model 3340, nicknamed the "Winchester",
is introduced. With a capacity of 60 MB it introduces several key technologies that lead to
it being considered by many the ancestor of the modern disk drive.
First Eight-Inch Form Factor Disk (1979): IBM's model 3310 is the first disk drive with 8"
platters, greatly reduced in size from the 14" that had been the standard for over a
decade.
First 3.5" Form Factor Disk Drive (1983): Rodime introduces the RO352, the first disk
drive to use the 3.5" form factor, which became one of the most important industry
standards.
First 2.5" Form Factor Disk Drive (1988): PrairieTek introduces a drive using 2.5" platters.
This size would later become a standard for portable computing.
First 1.3" Form Factor Disk Drive (1992): Hewlett Packard's C3013A is first 1.3" drive.
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Both the capacity of the hard disk
drive (above) and the density of data
on the disk (left) have increased in a
log-linear fashion for the past 20
years. How long can that continue?
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Hard disks store changing
digital information in a
relatively permanent form.
They give computers the
ability to remember things
when the power goes out.
Electronics within the
hard disk drive controls
the read/write
mechanism and the
motor that spins the
platters.
They also assemble the
magnetic domains on
the drive into bytes
(when reading) and turn
bytes into magnetic
domains (when writing).
What was using a computer
like before hard disk drives?
In a word... inconvenient.
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Hard disk drive
Internal components
Hard disks
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Hard disk drive
Internal components
Hard disk drive
Internal components
Underneath the board are
the connections for the
motor that spins the platters,
as well as a highly-filtered
vent hole that lets internal
and external air pressures
equalize.
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2
Hard drive
The arm
The arm that holds the read/write
heads is controlled by the
mechanism in the upper-left
corner, and is able to move the
heads from the hub to the edge
of the drive--The arm on a typical
hard-disk drive can move from
hub to edge and back up to 50
times per second
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Hard drive
The arm
Ac
t
The platters, which typically
spin at 3,600 or 7,200 rpm
when the drive is operating.
This drive has three
platters and six
read/write heads
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ua
to
r
Arms with Read/Write heads
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Different coatings on
hard drive platter
Read / Write Heads
• The read/write heads convert binary data to electromagnetic pulses
when writing to the disk, or the reverse when reading.
Thin film platters are actually reflective; taking
photographs of them is like trying to take a
picture of a mirror!
• Floppy disk heads are larger and much less precise than hard disk
heads.
• Hard disks have track density of thousands of tracks per inch, while
floppy disks have track density of 135 tracks per inch or less.
• Floppy disk drives spin much slower than hard disks: a typical floppy
spins at 300 to 360 RPM instead of the 3600 RPM or more of hard
disks
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A thin film 5.25" platter (above) next to an
oxide 5.25" platter (below).
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The read/write head writes data onto the disk (floppy or hard) in concentric circles called
tracks. There are usually 1024 (210) tracks on each side of a disk. Data is written on each
disk surface so a drive with three disks has six separate recording heads. A program within
the hard disk makes the tracks on the sides of stacked disks appear continuous.
This illustration shows how area
density works.
This imaginary disk is divided into
left and right half, and then a top
and bottom half.
Read/Write
head
Arm
The left half shows low track
density and the right half high track
density. The upper half shows low
linear density, and the bottom half
high linear density.
tu
Ac
Combining them, the upper left
quadrant has the lowest area
density; the upper right and lower
left have greater density, and the
bottom right quadrant of course
has the highest density.
r
at o
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Disk Anatomy
Disk Data Density
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The arm can move from the centre to the edge of the platter 50 times a second
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Disk Anatomy
Head Assembly
The disk is further divided into pie shaped segments. The intersection of a segment and a
track produces a sectors. Sectors are the smallest physical storage unit on a disk and
usually contain 512 bytes. The same track on stacked disks use to be called a cylinder.
Each platter has two sides; the top to record data, the bottom side contains track-positioning
information. The same track on stacked disks can be called a cylinder.
Side views
Platter
Data track
Magnetic
coating
3 Stacked platters
(disks)
Top (Side 0)
Bottom (Side 1)
es
On
MOTOR
nt
me
eg
Data track
on bottom
MOTOR
Tracks stacked
to form a
virtual
cylinder
One sector
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Disk Anatomy
one
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Disk Anatomy
The disks rotates at a constant speed (e.g., 7,200 rpm), but since the length of an inner
sectors is shorter than an outer sectors, the linear speed at which the read/write head moves
over the sector varies with distance from the center.
Read/Write
head
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The sector is divided into different sections. The first is an area to synchronize data
management, the second identifies the starting address of the sector and comes
before the actual data. The last section contains an error checking algorithm.
Outer
(fast)
For timing
Sync Area
One track with many sectors
Arm
three
tu
Ac
r
at o
To compensate for the difference in
rotational speed, the density of data in the
inner sectors is higher than in outer
sectors so that the same amount of data
is written or read over the same period of
time from any track
A cluster of 8 sectors
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Data Area (512 bytes)
Inner
(slow)
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Disk Formatting
Before a disk can be used for storage, the disk must first be formatted.
Large hard disks can be partitioned, divided into logical drives.
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Header
CRC Values
Contains
sector
address
Error correction
To optimize file storage, data is initially written in a number
of continuous sectors called a cluster. There can be 1, 2, 4,
8, etc. (2n) sectors in a cluster. Designating sectors in
clusters protects them from being over-written.
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Measuring the performance of
a hard disk
Low-level format (LLF): Factory formatting of the disk surface
to install characters like sector numbers that are used by the disk
controller hardware. LLF can not be done by the user.
Data transfer rate - The rate in bytes per second that the drive can
deliver data to the CPU. Rates between 5 and 40 megabytes per
second are common.
“Low-level format” is really reinitialization to factory
configuration. It involves identifying and removing defector
sectors and writing 0’s onto disk (zero-filling) it absolutely,
completely, permanently erases all data.
Seek time - The time for the actuator assembly to physically move to
the correct track (about 8 ms).
High-level or Quick format: deletes the FAT (File Allocation
Table) & creates a new directory. There is a chance that data can
be restored.
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Latency (Rotational delay) - the time required for the addressed area
of the disk to rotate into a position where it is accessible by the
read/write head (about 8 ms).
Capacity of the drive; the number of bytes it can hold (up to 1 TB).
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4
Latency
Hard Disk Interfaces
Interface type
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The time after the actuator assembly has completed
its seek to the correct track while the drive waits for
the correct sector to come around to where the
read/write heads are located is called latency
Maximum
possible data
transfer rate
(MBps)
Original IDE
2.1
Standard SCSI
5.0
EIDE (ATA-2)
16.6
Ultra SCSI
20.0
Ultra ATA (Ultra DMA)
33.3
Ultra Wide SCSI
40.0
Ultra160 SCSI
160.0
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As speeds continue to increase, there are diminishing
returns for the extra RPMs.
Going from 5,400 RPM to 7,200 RPM shaved 1.4
milliseconds off the average latency, but going from
7,200 to 10,000 (which is a bigger jump in both
absolute and percentage terms) only reduces it 1.2
milliseconds.
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Access Time
Access Time is the metric that represents the composite
of all the other specifications reflecting random
performance positioning in the hard disk.
Attribute
Best-Case Figure
(ms)
Worst-Case Figure
(ms)
Command
Overhead
0.5
0.5
It is a derived figure; comprised of the other positioning
performance specifications.
Seek Time
2.2
15.5
The most common definition of Access Time is:
Settle Time
<0.1
<0.1
Latency
0.0
8.3
Total
2.8
28.4
Access Time =
Command Overhead Time + Seek Time + Settle Time + Latency
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Hard drive and CPU interacting
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Disk Fragmentation
Highly simplified example
Over time the data that was initially written in sequential segments (a cluster), becomes
fragmented and scattered over the disk due to deletions, additions and rewrites. This is
fragmentation of the data.
When a command is made to store some data on a disk, the following chain of events occurs:
1.) The data flows into a cache where it is encoded using special mathematical formulae, ensuring
that any subsequent errors caused by noise can be detected and corrected.
2.) Free sectors on the disk are selected and the actuator moves the heads over those sectors just
prior to writing. (The time it takes the actuator to move to the selected data track is called the "seek"
time.)
3.) Once over the data track, the heads must not write the data until the selected free sectors on that
track pass beneath the head. This time is related to the rotation speed of the disk: the faster the
speed, the shorter this "latency" period.
4.) When it's time to write, a pattern of electrical pulses representing the data pass through a coil in
the writing element of the recording head, producing a related pattern of magnetic fields at a gap in
the head nearest the disk. These magnetic fields alter the magnetic orientations of bit regions on the
disk itself, so the bits now represent the data.
When a command is made to read some data on a disk, a similar process occurs in reverse. After
checking to see if the information is already in the hard disk's own internal buffer, the table of stored
data locations in the drive's electronics is consulted, the actuator moves the head over the track
where the chosen data is located, and the data is read.
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5
Disk De-Fragmentation
Fragmentation and Defragmentation
It take much longer to read fragmented data. So the disk should be periodically
defragmented, a process by which the computer retrieves data, and rewrites it in continuous
segments (a new cluster).
Disk fragmentation occurs when related data is stored in different location of
the hard disk. Defragmentation is typically used to refer to the Microsoft
Windows utility called Disk Defragmenter. It is designed to solve a problem
that occurs because of the way hard disks store data.
1. Hard disks store data in chunks called sectors. If you imagine the surface
of the disk divided into rings (like the rings of a tree), and then imagine dividing
each ring into pie-slices, a sector is one pie-slice on one ring. Each sector
holds a fixed amount of data, like 512 bytes.
2. The hard disk has a small arm that can move from ring to ring on the
surface of the disk. To reach a particular sector, the hard disk moves the arm
to the correct ring and waits for the sector to spin into position.
3. Hard disks are slow in computer terms. Compared to the speed of the
processor and its memory, the time it takes for the arm to move and for a
sector to spin into place is a comparatively long time; an eon. Periodically
defragmenting the hard disk will minimize this delay.
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Scan Disk & Defragmenter
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Using ScanDisk
A number of
utilities are
available to
maintain the
‘health’ of the
hard disk.
The ScanDisk utility
can check the disk for
errors and correct
some of them. The
error correction
algorithm at the end of
each sector can help
correct errors in the
data the sector
contains. Faulty sectors
can be identified and
labeled.
The exact path
to ‘Disk
Defragmenter’
may be slightly
different with
the version of
the operating
system you are
using.
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Disk Cleanup XP
Using Disk Defragmenter
• Go to Startup Î All
Programs Î Accessories
Î System Tools Î Disk
Cleanup
• Select Disk Cleanup tab
to delete temporary files
and logs
• Select More Options tab
to uninstall software not
used
The Defragmenter utility rewrites fragmented data into new clusters.
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6
How to be a Happy Disk User
Disk cleanup on a Mac OS X
OnyX: Disk utilities
• Organize files and folders
– Separate system, applications, utilities, and documents
into different partitions or folders.
• Periodically cleanup the disk
– Get rid of obsolete programs, files, etc.
•
•
•
•
Periodically defragment the drive
Check for viruses (Uses most current version)
Periodically Backup (you can’t do it afterwards!)
On crash/accidental erasure:
–
–
–
–
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Data recovery
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Internal drives use an SCSI or an EIDE interface:
•SCSI (Small Computer System Interface, pronounced "scuzzy"):
SCSI interfaces are faster than EIDE, but are also more expensive
and more complicated to install. You must have a SCSI interface card
installed in your PC to use a SCSI device.
– For Windows XP: R-Studio
– For Mac OS X: Stellar Phoenix
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Internal or External Storage
There are software that can read the HD
at a “low-level,” and potentially find
and recover pieces of files and data.
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Do not touch except with recover software
Run disk utility
Low level reformatting
Use the hard drive as a paperweight
•EIDE (Enhanced Integrated Drive Electronics): EIDE interfaces
boast Plug and Play capability, which means that Windows 95 or
higher will automatically recognize your new CD drive, making the
installation process quick and easy.
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External Storage
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Internal Hard Disk Storage
PCMCIA (PC Card), USB, and FireWire interfaces:
PCMCIA (Personal Computer Memory Card International
Association): PCMCIA cards, are credit card-sized devices
that slides into a PC Card slot
USB (Universal Serial Bus): USB interfaces are faster than
parallel ports, but slower than PCMCIA interfaces. Your
computer automatically recognizes any USB device when
it's plugged in. Up to 127 devices can be added to one USB
port. The newer USB 2 has a transfer rate of 480 Mbps
FireWire, or IEEE1394, is a fast connector that can transfer
data at up to 400 Mbps. A single FireWire port can connect
up to 63 external devices. New Firewire: 800 Mbps
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80 GB 7200 RPM EIDE
$47
750 GB 7200 RPM SATAII
interface $450
750 GB SATA NCQ
7200 RPM $190
Most computers come with EIDE (Enhanced IDE: Integrated Disk Electronics) built
into the motherboard. IDE and SCSI (Small Computer System Interface) disks
operate at the same speed, but SCSI has advantages over IDE as a multitasking
server because it allows many devices to be performing operations at the same
time. SATA (Standard Serial Advanced Technology Attachment). NCQ (Native
Command Queuing) is a newer version of SATA that improves data access.
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7
External Hard Disk Storage
Disk Data Density
Magnitude of information storage
1 byte = 8 bits = single alpha/numeric character
320 GB USB 2.0
Portable Hard
Drive $169
500 GB USB 2.0/
FireWire External
Hard Drive $169
1 kilobyte (KB) = 1024 bytes = a paragraph
250 GB 7200 RPM
Desktop USB 2.0
External Hard Drive $89
1 megabyte (MB) = 1024 KB = a medium paperback novel
1 gigabyte (GB) = 1024 MB = 30 feet of books
1 terabyte (TB) = 1024 GB = A large library, paper from 50,000 trees
1 petabyte (PB) = 1024 TB = Every book in every US library
1 TB 7200 RPM Hi-Speed
USB 2.0 External Desktop
Hard Drive $239
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1 TB 7200 RPM USB 2.0
Remote Access Storage - $360
1 exabyte (EB) = 1024 PB = All words spoken by humans since 5,000 BC
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Current prices for desktop computer
$499
$699
$799
Processor/Display
Processor/Display
Processor/Display
Processor/Display
AMD Athlon™ 64 X2 Dual-Core
4000+
AMD Athlon™ 64 X2 Dual-Core 5000+
Intel Core 2 Quad Processor Q6600
(8MB L2 cache,2.4GHz,1066FSB)
Intel Core 2 Quad Processor Q6600
(8MB L2 cache,2.4GHz,1066FSB)
Operating System
Operating System
Operating System
Operating System
Genuine Windows Vista® Home
Premium - English
Genuine Windows Vista® Home
Premium - English
Genuine Windows Vista® Home
Premium - English
Video Cards
Video Cards
Video Cards
Video Cards
NVIDIA GeForce 6150 SE
Integrated Graphics GPU
NVIDIA GeForce 6150 SE Integrated
Graphics GPU
Integrated Intel Graphics Media
Accelerator 3100
128MB NVIDIA GeForce 8300GS
Memory
Memory
Memory
Memory
1GB3 Dual Channel DDR2 SDRAM
at 667MHz- 2DIMMs
2GB3 Dual Channel DDR2 SDRAM at
667MHz- 2DIMMs
2GB3 Dual Channel DDR2 SDRAM at
667MHz- 2DIMMs
3GB Dual Channel DDR2 SDRAM at
667MHz - 4 DIMMs
Hard Drives
Hard Drives
Hard Drives
Hard Drives
320GB6 Serial ATA Hard Drive
(7200RPM) w/DataBurst Cache™
320GB6 Serial ATA Hard Drive
(7200RPM) w/DataBurst Cache™
500GB6 Serial ATA Hard Drive
(7200RPM) w/DataBurst Cache™
Monitor
Monitor
Monitor
Monitor
17 inch SE178WFP Widescreen
Flat Panel Monitor
19 inch SE198WFP Widescreen Flat
Panel Monitor
20 inch E207WFP Widescreen Digital
Flat Panel
20 inch E207WFP Widescreen Digital
Flat Panel
Optical Drive
16x DVD+/-RW Drive
Optical Drive
Optical Drive
16x DVD+/-RW Drive
16X DVD+/-RW Drive
Optical Drive
16X DVD+/-RW Drive
Security Software
Security Software
Security Software
Security Software
No Subscription (only 30-day
protection)
No Subscription (only 30-day
protection)
No Subscription (only 30-day
protection)
No Subscription (only 30-day
protection)
Office Productivity Software
(Pre-Installed)
Office Productivity Software (PreInstalled)
Office Productivity Software (PreInstalled)
Office Productivity Software (PreInstalled)
Microsoft Works 8. DOES NOT
INCLUDE MS WORD
Microsoft Works 8. DOES NOT
INCLUDE MS WORD
Microsoft Works 8. DOES NOT
INCLUDE MS WORD
Warranty & Service
Warranty & Service
Warranty & Service
Warranty & Service
1Yr In-Home Service,5 Parts +
Labor,4 24x7 Phone Support
1Yr In-Home Service,5 Parts + Labor,4
24x7 Phone Support
2Yr In-Home Service,5 Parts + Labor,4
24x7 Phone Support
2Yr In-Home Service,5 Parts + Labor,4
24x7 Phone Support
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Microsoft Works 8. DOES NOT
INCLUDE MS WORD
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Unlike the floppy and hard disk that uses magnetic media
to record data in discrete sectors, a compact disk uses a
small laser to write data onto the disk in a continuous
spiral. The spiral starts near the center and moves
outward. It is 0.5 microns wide and about 5 km (3.5 miles)
long.
Short bursts of light from the laser alters the reflective
properties of the disk in very small spots (pits). The data is
read off the disk as transitions in intensity between the pits
and adjacent areas (lands), not as the absolute intensity of
the reflected light from the land or pits. A transition between a
pit and land (or from land to pit) is decoded as a 1, while no
change indicates a zero. NRZI (non-return-to-zero inverted)
encoding.
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Sony and Philips Consumer Electronics set up a joint venture in 1979 to
design a new digital audio disc that would hold 60 min of music. Philips
developed a format on a 115 mm diameter disk, while Sony used a 100
mm disk. According to some sources, the president of SONY wanted the
disk to hold the 74 min performance of Beethoven’s 9th symphony.
A 120 mm diameter disk would be required to hold 74 min of music; the
120 mm disk is now the standard size.
Like the rotating hard disk, the linear speed of the CD
near the center of the disk is slower than near the outer
edge. However, instead of varying the amount of data
(the density of data) that is written onto a sectors to
maintain the same rate of data transfer, as is done with
the hard disk, the CD player varies the speed at which
disc spins as the read/write head moves from the center
to the edge. It slows the rotational speed down as the
read/write head (laser) moves outward.
In reality, Philips had a factory ready to produce large numbers of 115
mm disks while Sony did not have the production capacity to counter their
advantage by producing 100 mm disks. Remember their Betamax vs.
VHS competition in the 1980’s where Sony’s Betamax format for the VCR
was displaced by the VHS format. Forcing Philips to adopt the
120 mm standard allowed Sony time to build production capacity and
nullified Philips’ initial advantage.
CA are copied commercially by stamping the metallic
layer of the disk with a negative metal die to produce the
million of pits needed to contain 78 min of music. A
transparent coating is then applied to protect the pitted
surface. This ‘stamping’ process is very similar to the
one that was used to produce vinyl records.
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Compact Disk
Compact Disk
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Compact Disk
$999
Genuine Windows Vista® Home
Premium - English
250GB6 Serial ATA Hard Drive
(7200RPM) w/DataBurst Cache™
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8
Why would I want a new CD-Drive?
Flash card media
Because your existing CD-ROM drive:
• Produces hiccups or short pauses in your video
• Cannot read discs created by a CD-Recorder or CD-Rewriter
• Is 20-speed (20x) or less
A faster CD drive transfers data more
quickly, resulting in smoother video
displays. They read regular CD-ROMs as
well as create virtually lifelong records of
data on discs that can store up to 700MB
of data or 80 minutes of music.
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Flash memory is non-volatile memory that can be electrically erased
and rewritten. It is a specific type of EEPROM (Electrically Erasable
Programmable Read-Only Memory) in that it is rewritable. It is made
up of arrays of floating-gate transistors.
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USB FLASH MEMORY
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USB FLASH MEMORY
The most common form of flash memory is as a USB Flash Drive
1 USB connector
A USB Flash Drive is not a drive that has a rotating
disk. It is called a drive because it appears to the
computer operating system in the same way as a
mechanical disk drive, but it is a solid state device
with no moving parts.
2 USB mass storage controller device
(a small CPU)
3 Test points
4 Flash memory chip
5 Crystal oscillator (clock)
This lack of moving parts make
the flash drive very robust and
greatly reduces the amount of
power it needs. Most USB flash
drives draw all their necessary
power through the USB connection.
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6 LED (indicates when operating)
7 Write-protect switch (manual switch)
8 Space for second flash memory chip
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USB FLASH MEMORY
Flash Memory as USB ikura sushi
Digital audio player in a flash drive form
Flash Memory as an iPOD Nano
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Types of Storage
Flash drives come in various, sometimes bulky or novelty, shapes and sizes
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• Storage refers to the media used to store data and
software in a permanent form.
• Contrary to memory (RAM), information in storage
does not disappear when the computer is turned off.
• Several different types of technology and media are
used for storage:
–
–
–
–
–
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Paper tapes, cards (historical)
Magnetic tape, disks, diskettes
Optical
Magneto-optical
PC cards, flash cards, SD cards, CF cards
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9