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20 September

20 September . How Computers Have Affected Society. 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.

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20 September

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  1. 20 September How Computers Have Affected Society

  2. 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

  3. 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

  4. Homework review

  5. Two’s complement: both positive and negative • Two’s complement represents both positive and negative numbers 24 = 0000 0000 0001 10002 -24 = 1111 1111 1110 01112 + 12 1111 1111 1110 10002

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

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

  8. Cases 2 and 3 • Positive numbers are always greater than negative numbers

  9. 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? • 1010101012 • 110101012

  10. 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 01112 vs. 0010 01112 • 0111 01112 vs. 0111 11112

  11. 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

  12. Homework assignment (#14) • First is negative and second positive -> means second is larger • 1001 0001 1011 10112 0110 1001 0001 10112 • Subtract 2nd from first • 1001 0001 1011 10112 (1st) • 1001 0110 1110 01012 (-2nd) • 1010 1000 1010 00002 • But this is an overflow condition: carried a 0 in and a 1 out • Subtract 1st from 2nd • 0110 1001 0001 10112 (2nd) • 0110 1110 0100 01012 (-1st) • 1101 0111 0110 00002 • But this is an overflow condition: carried a 1 in and a 0 out • Need to extend to avoid overflow • Subtract 2nd from first • 1111 1001 0001 1011 10112 (1st) • 1111 1001 0110 1110 01012 (-2nd) • 1111 1010 1000 1010 00002 • Negative number means second is larger • Subtract 1st from 2nd • 0000 0110 1001 0001 10112 (2nd) • 0000 0110 1110 0100 01012 (-1st) • 0000 1101 0111 0110 0000v • Positive number means first (second in the problem) is larger • Decimal values: -28,229 and 26,907

  13. Homework assignment (#15) • Both are negative numbers • 1001 0001 1011 10112 1001 0001 1011 10112 • Subtracting • 1001 0001 1011 10112 (1st) • 0101 0110 1110 01012 (-2nd) • 1110 1000 1010 00002 negative number: means second is larger • Convert and compare • 1001 0001 1011 10112 (negative) • 0110 1110 0100 01012 (positive) • 1001 0001 1011 10112(negative) • 0101 0110 1110 01012 (positive) • First is larger positive value, which makes the second the larger negative number • Decimal values: -28,229 vs. -5,349

  14. Homework assignment (#16) • Both are positive numbers • 0001 0001 1011 10112 0010 1001 0001 10112 • Compare strings • 0001 0001 1011 10112 • 0010 1001 0001 10112 • Second is larger since it has the first 1 • Subtracting • 0001 0001 1011 10112 (1st) • 1101 0110 1110 01012 (-2nd) • 1110 1000 1010 00002 negative number: means second is larger • Decimal values: 2,299 vs. 10,523

  15. 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

  16. 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?

  17. Test • Sharing: what you think will be on the test

  18. Impacts that you recognize • Personal Impact • Community Impact • National Impact • Global Impact • Future Impact

  19. 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

  20. Community Impact • employment • traffic control • urban planning • law enforcement

  21. 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

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

  23. 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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