Transcript of Discovering Computers Chapter 7 Storage. 2 Ch 4 Processor Control Unit Arithmetic Logic Unit (ALU)...
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- Discovering Computers Chapter 7 Storage
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- 2 Ch 4 Processor Control Unit Arithmetic Logic Unit (ALU) Input
Devices Ch 5 Storage Devices Ch 7 Output Devices Ch 6 Memory
DataInstructions Information Instructions Data Information
Instructions Data Information Control Unit Ch 1 Introduction Ch 2
Internet & WWW Ch 3 Application Software Ch 8 System
Software
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- Writing Transfers items from memory to storage media Writing
Transfers items from memory to storage media What a storage device
does? Reading Transfers items from storage media to memory Reading
Transfers items from storage media to memory Hardware that writes
writes records to the medium holds them and reads from 4
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- 5 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
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- 6 Storage device and a storage medium storage medium Physical
material on which a computer keeps info storage device Hardware
that records, holds and retrieves items to and from a storage
medium
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- 7 How does storage differ from memory ? To work with a file,
you read a part (a block of records) from storage (block by block)
and place it in memory When you are finished with the block of a
file, you write it from memory to the storage Stores items for
future use, rather than current use Stores for a long time, rather
than temporarily Storage is nonvolatile, rather than volatile
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- 8 How does volatility compare? Contents of storage retained
when power is off - nonvolatile Screen display and contents of RAM
are volatile erased when power is off Screen display and contents
of RAM are volatile erased when power is off
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- 9 What is capacity? Number of bytes storage medium can hold
Storage Term Number of bytes Kilobyte Megabyte Gigabyte Terabyte
Petabyte KB MB TB GB PB 1 thousand 1 million 1 billion 1 trillion 1
quadrillion Abbreviation
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- Google believes that the plummeting price of storage will allow
iPods of the future (2020 A.D. ) to hold any video ever
produced.
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- Access time: The amount of time it takes a storage device to
locate an item on a storage medium 12
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- 13 Memory (RAM) Flash memory Compact disk Tape Hard Disk cost
less expensive more expensive speed faste r slower What is access
time? Amount of time it takes device to locate block on disk
measured in millisec / microsec / nanosec / picosec
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- Floppy DiskSmall files to be transported Secondary Storage
Primary Storage Hard Disk Flash Memory Cards and USB Flash Drives
CDs and DVDs Tape Items waiting to be interpreted and executed by
the processor Operating system, application software, user data and
information Digital pictures or files to be transported Software,
backups, movies, music Backups Memory (most RAM) What is transfer
rate? Time required to deliver a block from storage to memory in
kilobytes/sec (KB/sec) or megabytes/sec (MB/sec) faster transfer
rates slower transfer rates 14
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- Hard disk contains one or more inflexible, circular platters
that use magnetic particles to store data, instructions, and
information 15
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- Characteristics of a hard disk: 17 CapacityPlatters Read/Write
Heads Cylinders Sectors and Tracks Revolutions per Minute Transfer
Rate Access Time
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- Sample: Hard Disk Characteristics Advertised capacity500 GB
Platters4 Read/write heads8 Cylinders16,383 Bytes per sector512
Sectors per track63 Sectors per drive973,773,168 Revolutions per
minute7,200 Transfer rate300 MB per second Access time8.5 ms
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- 19 Calculating capacity of a hard drive Sector stores 512 bytes
of data 16383 cylinders times 8 tracks in a cylinder times 63
sectors per track times 512 bytes per sector = 500 GB
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- 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) 22
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- 23 Hard Disk Terminology Platter Track SectorHeadArm
Cylinder
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- platter read/write head platter sides cylinder track sector
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- 26 Track is the narrow recording band that forms full circle on
disk surface Cylinder is the collection of single tracks through
all platters Single movement of read/write head arms can read any
track on the cylinder track cylinder
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- What is a head crash? Spinning creates cushion of air that
floats read/write head above platter Occurs when read/write head
touches platter surface A smoke particle, dust particle, or human
hair could render drive unusable 27
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- 28 How does RAID work? Redundant Array of Independent Disks
Disk system that duplicates data, instructions, and information to
improve data reliability mirroring (RAID Level 1) Mirroring has one
backup disk for each primary disk
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- External hard disk freestanding hard disk that connects to
system unit Removable hard disk you insert and remove from hard
disk drive 29
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- What is a disk cache ? Portion of memory that processor uses to
store frequently accessed items second request for data goes to
hard disk first request for data goes to disk cache 30
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- 31 Disk History 1973: 140 MB 1979: 2,300 Mbytes = 2.3 GB
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- 32 1 inch disk drive! v Hitachi 2007 release Development driven
by iPods & digital cameras 20GB, 5-10MB/s
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- Flash Memory Storage Flash memory chips contain no moving parts
solid state drives; they have several advantages over magnetic hard
disks: 33 Faster access time Faster transfer rates Generate less
heat and consume less power Last longer
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- USB flash drives plug into a USB port on a computer or mobile
device 34
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- A memory card is a removable flash memory that you insert and
remove from a slot in a computer 36 CompactFlash (CF) Secure
Digital (SD) Secure Digital High Capacity (SDHC) microSDmicroSDHC
xD Picture Card Memory Stick Memory Stick Micro (M2)
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- What are PC Cards? Add capabilities to computer
Credit-card-sized device commonly used in notebook computers
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- What is a smart card? Stores data on microprocessor embedded in
small card Input, process, output, and storage capabilities 39
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- Cloud Storage 40
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- 41 Security Allows offsite backups of data Share Others can be
authorized to access data from your Internet hard drive
Accessibility Files can be accessed from any computer or device
with Web access When in need Large audio, video, and graphics files
can be downloaded to an Internet hard drive What are advantages of
an Internet storage?
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- Reasons to subscribe to cloud storage: 42 Access files from any
computerStore large filesAllow others to access their filesView
data and imagesStore offsite backupsProvide data center
functions
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- Push the same button to close the tray. What are optical discs?
Most PCs include an optical disc drive Flat, round, portable discs
made of metal or plastic Can be read only or read/write Insert the
disc, label side up. Push the button to slide out the tray. 43
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- How does a laser read data on an optical disc? laser diode
prism light- sensing diode 01 lens pitland disc label Step 1. Laser
diode shines a light beam toward disc. Step 2. If light strikes a
pit, it scatters. If light strikes a land, it is reflected back
toward diode. Step 3. Reflected light sends digital signals of 1 to
computer. Absence of reflected light is read as digital signal of
0. 44
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- How is data stored on an optical disc? Data is stored in single
track Track divided into evenly sized sectors that store items
single track spirals to edge of disc disc sectors 45
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- How should you care for an optical disc? 46
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- What is the data transfer rate of a CD drive? Ranges from 48X
to 75X 75X 75 150 KBps = 11,250 KBps or 12.25 MBps X is 150 KBps
(KB per second ) 48X: 48 150 KBps = 7,200 KBps or 7.2 MBps 47
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- A CD-ROM can be read from but not written to A CD-R is an
optical disc on which users can write, but not erase A CD-RW is an
erasable disc 48
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- 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 software 49
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- What are CD-Rs and CD-RWs? Must have CD recorder or CD-R drive
Cannot erase discs contents CD-R (compact disc-recordable) you can
write on once CD-RW (compact disc-rewritable) disc you can write on
multiple times Must have CD-RW software and CD-RW drive 50
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- What is a DVD-ROM (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 100 GB HD-DVD discs have storage capacity of up to 60 GB
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- Other Types of Storage 52
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- What is a tape? Magnetically coated plastic ribbon capable of
storing large amounts of data at low cost Used for backup 53
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- 54 What is sequential access versus direct access? sequential
access Reading and writing data consecutively Method used for tape
direct access You can locate a particular data item or file
immediately Method used for hard disks, and compact discs Also
called random access
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- How is data stored on a tape? Sequential access Unlike direct
access ( used on hard disks, CDs, and DVDs ) which can locate
particular item much faster Reads and writes data consecutively,
like music tape 55
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- A magnetic stripe card contains a magnetic stripe that stores
information A smart card stores data on a microprocessor embedded
in the card 56
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- Microfilm and Microfiche Images are recorded using computer
output microfilm recorder 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 57
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- Enterprise storage stores huge volumes of data and information
for large businesses Uses special hardware for heavy use, maximum
availability, and maximum efficiency 59
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