Lecture4 2.8 3.4

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Lecture-4 (2.8 3.4)

• CSCI130-03A
• Instructor Dr. Imad Rahal

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Announcements

• Quiz 1 next Friday
• Closed book/notes, no calculators, and no
  computers
• Assignment 1 due Tuesday 13th
• Try to finish it before quiz
• Go to
• My Computer
• N
• CS130
• Handouts
• NumberConversion.doc

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Non-numeric Data Representation

• Picture/Image Data
• Divide the screen into a grid of cells each
  referred to as a pixel
• 512156 image ? grid has 512 columns and 256 rows
• How many pixels?
• Pixel values and sizes depend on the type of the
  image
• For black white images, we can use 1 bit for
  every pixel such that 1 ? black and 0 ? white
• For grayscale images, we use 1 byte where 255 ?
  black and 0 ? white and anything in between is
  gray (higher/lower values are closer to
  black/white)
• For color images, we need three values per pixel
  (depends on the color scheme used)
• Red/Green/Blue
• We need 1 byte per value ? 3 bytes per pixel
• For an 512x256 image
• 512x256x3 384K bytes

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Assume all images have 512x256 resolution. Can
you find their sizes in bytes?
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Non-numeric Data Representation

• Image movies are built from a number of images
  (or frames) that are displayed in a certain
  sequence at high speeds
• 30 frames per second
• 2-hr movie needs (assume previous image used)
• 384K 30 60 120 83 GB (billion) bytes!
• People use compression to reduce large movie
  sizes
• Usually the change between two consecutive images
  is small ? store only difference between frames
  (Temporal compression)
• Large areas with the same color can be stored by
  saving the boundary pixels only (everything
  within the boundaries has the same value)
  (Spatial compression)

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Non-numeric Data Representation
The heard sound depends on the altitude and
frequency

• Sound/Audio Data
• An object produces sound when it vibrates in
  matter (e.g. air)
• A vibrating object sends a wave of pressure
  fluctuations through the atmosphere
• We hear different sounds from different vibrating
  objects because of variations in the sound wave
  frequency
• Higher wave frequency means air pressure
  fluctuation switches back and forth more quickly
  during a period of time
• We hear this as a higher pitch (intensity)
• When there are fewer fluctuations in a period of
  time, the pitch is lower
• The level of air pressure in each fluctuation,
  the wave's amplitude or height, determines how
  loud the sound is

Volts
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Non-numeric Data Representation

• Numbers used to represent the amplitude of sound
  wave
• Analog is continuous and we need digital
• Digitize the sound signal
• Measure the voltage of the signal at certain
  intervals (e.g. 40,000 per sec for CDs)
• Reconstruct wave
• Compression can also be used for audio files
• MP3 reduces size to 1/10th
• ? faster transfer over the Internet

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Non-numeric Data Representation

• Digital image and audio have a lot of advantages
  over non-digital ones
• Can easily be modified by changing the bit
  pattern
• Image enhancement, noise/distortion removal, etc
  
• Superimpose one sound on another or image on
  another results in newer ones

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Non-numeric Data Representation

• It makes you wonder if images can be trusted

• adapted from a course offered at BU

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Non-numeric Data Representation
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Data Storage (3.1 3.3)
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Overview of Computer Hardware

• Read 3.1 - 3.3
• What are the necessary components of a computer
• CPU, Main memory
• What are the components that we need for
  convenience
• Otherwise the computer wont be very practical to
  use
• Secondary/Auxiliary storage, I/O devices

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Overview of Computer Hardware

• CPU
• Central Processing Unit
• Single silicon chip with circuits attached to it
• Known as microprocessor
• Sits on a circuit board known as the motherboard
• Main memory
• Connects to the motherboard
• Divided into two major parts
• RAM --- Random Access Memory
• Contains the memory registers which store data
  before/after CPU processing
• Available for users and programs so store data in
  and read data from ? very dynamic
• Volatile --- does not persist when no electric
  power is supplied to its circuits

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Overview of Computer Hardware

• ROM --- Read Only Memory
• Permanent
• Holds programs that are vital for the operation
  of the computer (such as boot and other System
  files)
• As the name indicates, can be read but never
  altered
• Cache
• A type of memory that sits between main memory
  and CPU
• Faster, smaller and more expensive than main
  memory
• Used a lot in mobile phones

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Overview of Computer Hardware

• Input devices
• Takes data from the user and converts it into
  binary
• Sends it to main memory
• Mouse, touch screens, scanners, digital cameras,
  etc

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Overview of Computer Hardware

• Output devices
• Devices such as monitors, speakers, printers, etc
  
• Monitors
• CRTs (cathode ray tubes) VS Flat-panel
• CRTS are cheaper (4-8 times less) and more used
  with desktops
• Three important monitor characteristics to watch
  out for
• Resolution number pf pixels on the screen...the
  higher the better (640x480 to 1600x1200)
• Dot pitch how close are the pixels to each
  otherthe closer the better (.2 or .3)
• Refresh rate number of times per second that a
  new electric pulse is sent to each pixel to
  maintain the color from fading (70Hz or higher)

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Overview of Computer Hardware

• Printers
• Two major types
• Laser VS ink-jet
• Both use small dots to form images of characters
  and graphics being printed
• Ink-jet however sprays smalls dots of liquid ink
  onto the page from a matrix of ink jets
• Laser creates an image of the page to be printed
  on cylinder (photoreceptor drum) covered with
  magnetically charged toner (powder ink)
• The image is created on the drum as a negative
  charge
• Toner (positive) is spread over the drum and
  sticks only to the image
• Paper is given a strong negative charge passes
  close to drum so that the powder leaves the drum
  and sticks to the paper

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Overview of Computer Hardware

• Auxiliary Storage
• Used to store data/programs for long terms
  (permanent storage)
• much slower and cheaper than main memory
• Tapes, disks and CDs
• Magnetic tape
• Like VHS films or cassettes
• Was ubiquitous prior to the 80s
• Nowadays, only for backup and archiving
• Cheap, holds a lot of data and easy to store
• Binary data from RAM is stored as is
• Thin plastic tape covered with a coating that
  accepts magnetic charge

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Overview of Computer Hardware

• A dot of magnetic charge is a 1, nothing is a 0
• Divided into multiple segments
• There is a directory that stores where (i.e. in
  which segment) every file is stored
• To access a file
• Mount tape on drive
• FF until the right segment
• Write or read
• Sequential access
• Start from the beginning and go all the way until
  the desired file is found
• Time consuming ? not used for storage in
  Computers

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Overview of Computer Hardware

• Magnetic Disk
• Used the most for permanent storage in computers
• In principal, stores data pretty much the same
  way as tapes
• Magnetic coating covers the disk
• Takes magnetic charge to represent data
• Divided into tracks and sectors
• Tracks are concentric circles on the disk each
  holding information that too big to fit in main
  memory
• Sectors divide the disk into pie-shaped areas
• Data fills all track within one sector

• All tracks can store the same number of bits!!!
• ? more compact towards the center

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(No Transcript)
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R/W Head

• R/W head can move to any position (sector, track)
  on the disk ? random access

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Overview of Computer Hardware

• Comes in two forms
• Portable
• Floppy disks
• Because they are flexible (easily bent)
• 3.5
• 1.44 MB
• Zip disks
• Several 100 MBs
• Accessed by a disk drive
• Need formatting sets up tracks and sectors and
  directory (where is every file) and erases
  everything

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Overview of Computer Hardware
Disk Pack

• Fixed
• Hard disks
• Single (PCs) or multiple ( 10 to 12)
• Multiple GBs per disk
• Diskettes have 135 tracks per inch and 18 tracks
• HDs have 1000s of tracks per inch and 64 tracks
• R/W does not touch the surface but floats right
  above it ? Rotate 100 times faster than diskettes
• They are sealed so that no dirt comes between R/W
  head and disk (corrupts data)

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Overview of Computer Hardware

• Compact Disks (CDs)
• Optical disk
• Data stored like magnetic disks (series of dots
  on tracks)
• Now we BURN the dots (rather than magnetic
  charges) as pits on the surface
• A laser detects those pits as 0s
• Data spans a track of the disk (not sectors)
• Pits gives the advantage of more density of
  storage
• 600 MB to 10 GB
• Most CDs are Read-only (because of the burning)
• Some optical drives do allow for re-burning of
  surface after smoothing out the pits

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Overview of Computer Hardware

• File Management
• To process data, computers copy a fixed amount of
  data from disk or tape to RAM
• Called a physical block
• Copied to buffer in RAM
• A file may fit into 1 (even if less) or more
  blocks (not always contiguous)
• In the latter case, the RAM may need to
  reassemble a file from several blocks on disk
• Done in part of RAM called buffer
• Magnetic and optical disks have directories that
  for every stored file
• Name
• Starting location (track, sector and possibly
  side)
• Length
• Directory also maintains a list of empty blocks

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Overview of Computer Hardware

• FYI when you delete a file, IT IS NOT DIRECTLY
  DELETED FROM DISK!!!
• The files entry in the directory is erased
• Its occupied space is added to the list of empty
  space
• The occupied space awaits to be written over by
  other data
• File organization
• Hierarchical
• Folders/directors (root)
• Tree-structured file system

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Data Manipulation (3.4)
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Data Manipulation

• Recall that adding and comparing bit patterns is
  sufficient to achieve an operational machines
• This is done by circuits for adding and comparing
  bit patterns in registers
• Circuits are made up of gates
• Gates and Truth Tables
• Gates needed are NOT, AND, and OR
• NOT Gate
• Single input and single output
• Reverses input
• 1 ? 0 and 0 ? 1
• If there is electric power ? shut it off
• If there is no electric power ? turns it on
• Like a power switch

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Data Manipulation

• AND Gate
• Accepts two inputs and yields one output
• Always 0 except when both are 1s
• Requires power coming from both lines in order to
  give out power

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Data Manipulation

• OR Gate
• Accepts two inputs and yields one output
• Always 1 except when both are 0s
• Requires power coming from at least one of the
  input lines in order to give out power
• Variant XOR
• 1 if inputs are distinct

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Data Manipulation

• These three simple gates are combined to create
  circuits that perform more complicated operations
• These new combinations can be expressed in three
  ways
• Through Expressions
• A AND B ? AB
• A OR B ? AB
• NOT A ? A
• (NOT A AND NOT B) OR (A AND B) ? AB AB