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Chapters 1,2,3, & 4 Quiz # 1 1

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2 Analog and Digital Information Information can be represented in one of two ways: analog or digital Analog data A continuous representation, analogous to the actual information it represents Digital data A discrete representation, breaking the information up into separate elements

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Digitization Initially transforming data for computer use Assigning people social security numbers The creation of telephone numbers Encoding information became the way to transform the real world into a context that the computer could understand

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Information Metamorphosis Fitting the real world into the computer Computers world –Electronic –Fast –Binary Real World –Multiple forms of data / information –Imprecise / vague –Non uniform speeds

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Information Metamorphosis Real World Data Forms –Numeric Data –Character Data –Graphical / Visual Data –Audio Data –Instructional Data Methodology needed to transform real world data into computer world (binary)

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Binary Number System Binary for numeric data Binary digit = Bit 8 Bits = Byte –Smallest addressable unit within the computer 4 Bytes = Word –Basic unit for arithmetic –Contains 32 bits Converting from binary

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Numeric Data Converting to binary –Repeated division by 2 –Remainders are the important part –Read from bottom up as if left to right

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Character Data Binary for Character Data –8 bit combinations assigned to a symbol –Name for mapping process is ASCII table

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Graphical Data Binary for Graphical Data

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Graphical Data Binary for Graphical Data

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Graphical Data Binary for Graphical Data Each black pixel is represented as a 1 Each white pixel is represented as a 0 Pixels are grouped in units of 8 so they can be stored in 1 byte

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Graphical Data A 1 picture scanned at 150 DPI (dots per inch) Total size = 150 X 150 22,500 dots Memory required = 22,500 / 8 2,813 bytes Color requires more bits to represent each dot Using 8 bits for each dot allows for 256 different colors The 1 picture now requires 22,500 bytes

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Graphical Data Printers are rated in DPI for print quality Scanners are rated in DPI for image resolution Monitors / displays have display settings for display resolution –800 X 600 –1024 X 768 –1280 X 1024 –1400 X 1050

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Audio Data Binary for audio data Sound as a waveform –Y-axis represents voltage –X-axis represents time Suppose the wave form shown represents 1 second of sound

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Audio Data Divide Sample into segments

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Audio Data Divide Sample into more segments

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Audio Data Divide Sample into even more segments

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Audio Data The more segments the better the re-created wave form The given sample was divided into 34 segments (approx) An Audio CD utilizes 44,000 samples per second of sound

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Instructional Data Binary for Instructional Data Instructional Data has not only content but sequence Driving directions to NJ Aquarium –Designated number of steps –Sequence of steps is critical to success –Rearranging sequence will not get you to the NJ Acquarium Recipe / Directions / Program

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20 The Unicode Character Set Extended ASCII is not enough for international use One Unicode mapping uses 16 bits per character How many characters can this mapping represent? Unicode is a superset of ASCII The first 256 characters correspond exactly to the extended ASCII character set

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21 Keyword Encoding Replace frequently used words with a single character

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22 Run-Length Encoding A single character may be repeated over and over again in a long sequence Replace a repeated sequence with –a flag character –repeated character –number of repetitions *n8 –* is the flag character –n is the repeated character –8 is the number of times n is repeated

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23 Huffman Encoding In Huffman encoding no character's bit string is the prefix of any other character's bit string To decode look for match left to right, bit by bit record letter when a match is found begin where you left off,going left to right

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24 Digitized Images and Graphics Digitizing a picture Representing it as a collection of individual dots called pixels Resolution The number of pixels used to represent a picture Raster Graphics Storage of data on a pixel-by-pixel basis Bitmap (BMP), GIF, JPEG, and PNG are raster- grahics formats

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25 Digitized Images and Graphics Bitmap format Contains the pixel color values of the image from left to right and from top to bottom GIF format (indexed color) Each image is made up of only 256 colors JPEG format Averages color hues over short distances PNG format Like GIF but achieves greater compression with wider range of color depths Which is better for line drawings? Pictures?

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26 Vector Graphics Vector graphics A format that describes an image in terms of lines and geometric shapes A vector graphic is a series of commands that describe a lines direction, thickness, and color The file sizes tend to be smaller because not every pixel is described

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27 Vector Graphics The good side and the bad side… Vector graphics can be resized mathematically and changes can be calculated dynamically as needed Vector graphics are not good for representing real-world images

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28 Computers and Electricity Gate A device that performs a basic operation on electrical signals Circuits Gates combined to perform more complicated tasks

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29 Computers and Electricity How do we describe the behavior of gates and circuits? Boolean expressions Uses Boolean algebra, a mathematical notation for expressing two-valued logic Logic diagrams A graphical representation of a circuit; each gate has its own symbol Truth tables A table showing all possible input value and the associated output values

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30 NOT Gate A NOT gate accepts one input signal (0 or 1) and returns the opposite signal as output Figure 4.1 Various representations of a NOT gate

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31 AND Gate An AND gate accepts two input signals If both are 1, the output is 1; otherwise, the output is 0 Figure 4.2 Various representations of an AND gate

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32 OR Gate An OR gate accepts two input signals If both are 0, the output is 0; otherwise, the output is 1 Figure 4.3 Various representations of a OR gate

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33 XOR Gate Figure 4.4 Various representations of an XOR gate An XOR gate accepts two input signals If both are the same, the output is 0; otherwise, the output is 1

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NAND Gate The NAND gate accepts two input signals If both are 1, the output is 0; otherwise, the output is 1 Figure 4.5 Various representations of a NAND gate

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35 NOR Gate Figure 4.6 Various representations of a NOR gate The NOR gate accepts two input signals If both are 0, the output is 1; otherwise, the output is 0

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36 Combinational Circuits Gates are combined into circuits by using the output of one gate as the input for another

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37 Combinational Circuits Three inputs require eight rows to describe all possible input combinations This same circuit using a Boolean expression is (AB + AC)

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38 Combinational Circuits Consider the following Boolean expression A(B + C) Does this truth table look familiar? Compare it with previous table

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39 Combinational Circuits Circuit equivalence Two circuits that produce the same output for identical input Boolean algebra allows us to apply provable mathematical principles to help design circuits A(B + C) = AB + BC (distributive law) so circuits must be equivalent

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40 Adders The result of adding two binary digits could produce a carry value Recall that 1 + 1 = 10 in base two Half adder A circuit that computes the sum of two bits and produces the correct carry bit Truth table

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41 Adders Circuit diagram representing a half adder Boolean expressions sum = A B carry = AB

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42 Adders Full adder A circuit that takes the carry-in value into account Figure 4.10 A full adder

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43 Circuits as Memory The design of this circuit guarantees that the two outputs X and Y are always complements of each other The value of X at any point in time is considered to be the current state of the circuit Therefore, if X is 1, the circuit is storing a 1; if X is 0, the circuit is storing a 0 Figure 4.12 An S-R latch

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44 Ethical Issues Email Privacy Explain why privacy is an illusion. Who can read your email? Do you send personal email from work? Does everyone in your family use email?

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