20 september how computers have affected society
TRANSCRIPT
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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 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
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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
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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
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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