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20 September How Computers Have Affected Society

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Spyware and Adware Spyware - programs that reside in hidden corners of a computer's hard drive and record confidential information like keystrokes, passwords and the user's history of Web site visits. Piggybacking onto other software programs that people download Sneaking through backdoor security gaps in Web browsers Technically agree to download the software Adware -- billboard pitches through online distribution with the possibility of immediate response CoolWWWSearch or CoolWebSearch changes its name and location on a hijacked computer several times a day - making it virtually impossible to track Impact Screens transformed into digital versions of Times Square Overburdened PC's that operate much more slowly Software solutions products like Spybot-Search & Destroy, Spy Sweeper and Adaware switch from Internet Explorer to Mozilla consumer complaints have become frequent and vociferous Internet “too accessible” Legislation or self-regulation? http://www.spywareguide.com/ http://www.nytimes.com/2004/09/19/business/yourmoney/19gator.html?pagewanted=3&th

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Assignments Project Dates Posted Oct 11: *Influence of Computers in _____ Oct 25: Web Page Nov 8: *Computers as Used in the Arts Nov 22: Database Dec 8: *How Computer Can Solve ____ *Written report and presentation Everyone will present on Dec 8 Choose which of the other 2 you want to present Sign up for leading news discussion Need to discuss topics with me…electronic or in person

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Homework review

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Two’s complement: both positive and negative Two’s complement represents both positive and negative numbers 24 = 0000 0000 0001 1000 2 -24 = 1111 1111 1110 0111 2 + 1 2 1111 1111 1110 1000 2

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Recognizing negative numbers In two’s complement, First digit = 1 -> negative First digit = 0 -> positive

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Comparing numbers Four cases: 1. Positive and positive 2. Positive and negative 3. Negative and positive 4. Negative and negative What would you do in base 10 in these four cases? While subtracting always works, it can be easier …

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Cases 2 and 3 Positive numbers are always greater than negative numbers

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Case 1: comparing positive numbers In base 10, which is larger, a 3-digit number or a 2-digit number? Consider 100 vs. 99 This is also true in any other base So, without any computation, which is larger? 101010101 2 11010101 2

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Comparing positive numbers algorithm Algorithm: Assuming two equal length strings, compare the strings from left to right First string with a 1 while the other has a 0 is larger 0100 0111 2 vs. 0010 0111 2 0111 0111 2 vs. 0111 1111 2

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Case 4: comparing negative numbers Two options Subtract If A – B > 0 than A is larger than B -10 - -20 = 10 (-10 > -20) If A – B < 0 than B is larger than A -25 - -15 = -10 (-15 > -25) Convert both numbers to positive equivalent. What is the base 10 rule? If A > B than -A < -B 20 > 10, -20 < -10

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Homework assignment (#14) First is negative and second positive -> means second is larger 1001 0001 1011 1011 2 0110 1001 0001 1011 2 Subtract 2 nd from first 1001 0001 1011 1011 2 (1 st ) 1001 0110 1110 0101 2 (-2 nd ) 1010 1000 1010 0000 2 But this is an overflow condition: carried a 0 in and a 1 out Subtract 1 st from 2 nd 0110 1001 0001 1011 2 (2 nd ) 0110 1110 0100 0101 2 (-1 st ) 1101 0111 0110 0000 2 But this is an overflow condition: carried a 1 in and a 0 out Need to extend to avoid overflow Subtract 2 nd from first 1111 1001 0001 1011 1011 2 (1 st ) 1111 1001 0110 1110 0101 2 (-2 nd ) 1111 1010 1000 1010 0000 2 Negative number means second is larger Subtract 1 st from 2 nd 0000 0110 1001 0001 1011 2 (2 nd ) 0000 0110 1110 0100 0101 2 (-1 st ) 0000 1101 0111 0110 0000v Positive number means first (second in the problem) is larger Decimal values: -28,229 and 26,907

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Homework assignment (#15) Both are negative numbers 1001 0001 1011 1011 2 1001 0001 1011 1011 2 Subtracting 1001 0001 1011 1011 2 (1 st ) 0101 0110 1110 0101 2 (-2 nd ) 1110 1000 1010 0000 2 negative number: means second is larger Convert and compare 1001 0001 1011 1011 2 (negative) 0110 1110 0100 0101 2 (positive) 1001 0001 1011 1011 2 (negative) 0101 0110 1110 0101 2 (positive) First is larger positive value, which makes the second the larger negative number Decimal values: -28,229 vs. -5,349

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Homework assignment (#16) Both are positive numbers 0001 0001 1011 1011 2 0010 1001 0001 1011 2 Compare strings 0001 0001 1011 1011 2 0010 1001 0001 1011 2 Second is larger since it has the first 1 Subtracting 0001 0001 1011 1011 2 (1 st ) 1101 0110 1110 0101 2 (-2 nd ) 1110 1000 1010 0000 2 negative number: means second is larger Decimal values: 2,299 vs. 10,523

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Algorithms “Put the numbers together” is insufficient. Why? Need to give an order Need to handle positive and negative numbers Since the instructions didn’t demand two’s complement, can use sign-magnitude

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One more thought Microsoft calculator can translate between bases Positive numbers work fine From negative decimal to binary or hexadecimal ok But can’t go back What’s happening?

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Test Sharing: what you think will be on the test

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Impacts that you recognize Personal Impact Community Impact National Impact Global Impact Future Impact

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Personal Impact human interactions leisure time communications relations knowledge medicine schools products accessibility for the handicapped privacy and personal rights data banks, computer terminals, data security employment job opportunities, new careers, the need for retraining telecommuting, always at work replacement of jobs business transactions automated billing, credit cards, consumer spending

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Community Impact employment traffic control urban planning law enforcement

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National Impact medicine communications media the use of information for control broadcasting elections electronic funds transfer stock-market transactions defense surveillance national data banks employment: shifting patterns move to information economy crime

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Global Impact reporting of current events world government international standards exploration of space and sea world wide access to data global economy

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Future Impact computers in the home Gaming, learning, electronic mail, shopping, business transactions, information processing, storage and retrieval the home as a work center effect on the family unit travel computer communication as a replacement how we travel possible disappearance of hard copy the cashless society the use of robots in industry and in the home

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