CSCI130

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Lecture 4 (3.1-3.5)

• CSCI130
• Instructor Dr. Imad Rahal

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Data Storage (3.1-3.3)
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Overview of Computer Hardware

• Quiz or team quiz
• necessary components of a computer
• CPU, Main memory
• components needed for convenience
• computer wont be very practical to use otherwise
• Secondary/Auxiliary storage, I/O devices
• CPU
• Central Processing Unit
• Single silicon chip with circuits attached to it
• Known as microprocessor
• Sits on a circuit board known as the motherboard

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Overview of Computer Hardware

• Main memory
• Connects to the motherboard
• Divided into two major parts
• RAM --- Random Access Memory
• memory registers which store data before/after
  CPU processing
• Available for users and programs so store data in
  and read data from
• Volatile --- does not persist when no electric
  power is supplied to its circuits
• ROM --- Read Only Memory
• Permanent
• Holds programs that are vital for the operation
  of the computer
• As the name indicates, can be read but never
  altered

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Overview of Computer Hardware

• 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
• Input devices
• Takes data from the user and converts it into
  binary
• Sends it to main memory
• Mouse, touch screens, scanners, digital cameras,
  etc
• Questions on output devices (printers and
  monitors), secondary storage (magnetic disks,
  tapes, and optical disks) or file management

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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
• 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 VS Optical
• What is a 1? 0?
• Sequential VS Direct
• Fast VS Slow
• E.g. of Magnetic disks

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Overview of Computer Hardware

• 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
• 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 (higher density)

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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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Data Manipulation (3.4)
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Data Manipulation

• Computing an answer to an equation
• 53 63 7 33/12
• Assume our computer cant directly multiply,
  subtract, or raise to power
• Multiplication task (Algorithm)
• 1 Get 1st number, Number_1
• 2 Get 2nd number, Number_2
• 3 Answer 0
• 4 Add Number_1 to Answer
• 5 Subtract 1 from Number_2
• 6 if Number_20, go to step 4
• 7 Stop

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Data Manipulation

• What we really need for this example
• Store numbers
• Add numbers (Subtract ?)
• Compare number
• All tasks done by a general-purpose computer can
  be accomplished through the following set of
  operations
• Store data
• numbers (positive, negative or fractions), text,
  pictures, etc
• Compare data (numbers, pictures, sounds, letters)
• Add
• Move data from one storage (memory) location to
  another
• Editing a text document
• Input/output
• Not mentioned in book but important

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Data Manipulation

• 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 logical 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 (or more) and yields one
  output
• Output is 0 when any input is 0
• 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
• Output is 1 when any input is 1
• 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
• Circuits, in turn, might then be used (thru
  programs) to perform even more complicated tasks
• Gate combinations can be expressed in three ways
• (1) Through Expressions
• A AND B ? AB
• A OR B ? AB
• NOT A ? A
• (NOT A AND NOT B) OR (A AND B) ? AB AB

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• Enough rows to hold all input combinations
• 1 letter ? 21 rows
• 2 letters ? 22 rows
• 3 letters ?23 rows
• n letters ?2n rows

• (2) Through Circuit diagrams
• Given an expression
• Try AB AB
• (3) Through Truth Tables
• Each of the representations can be derived from
  the other
• Derive truth table given expression
• One column for each letter
• Make 1 additional column for every sub-expression
  (order parentheses, NOTs, ANDs, ORs)