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20 September How Computers Have Affected Society
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Page 1: 20 September How Computers Have Affected Society.

20 September

How Computers Have Affected Society

Page 2: 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.

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 10002

-24 = 1111 1111 1110 01112

+ 12

1111 1111 1110 10002

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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 positive2. Positive and negative3. Negative and positive4. 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? 1010101012

110101012

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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 01112 vs. 0010 01112

0111 01112 vs. 0111 11112

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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 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 0101 2 (-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

Page 13: 20 September How Computers Have Affected Society.

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

Page 14: 20 September How Computers Have Affected Society.

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

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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

Page 18: 20 September How Computers Have Affected Society.

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