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CS 101 – Aug. 28 A little history Introduce binary numbers
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Before 1940s Only analog machines, moving parts Specific purpose –Adding machines –Tabulators –Sunrise/sunset, celestial General computing only theoretical interest –Alan Turing
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1940s Code-breaking machines in WW 2 General purpose electronic computers –ENIAC, U. of Pennsylvania –ABC, Iowa State –Z3, Konrad Zuse in Germany Transistor (1947) to have impact later von Neumann concept forms basis of computer organization
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US Army photo
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1950s & 1960s Commercially produced computers (IBM) –gradually become more common in industry Programming languages developed to facilitate commands to the machine Colleges begin to teach computing Large and expensive Moore’s Law
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1970s & 1980s Integrated circuit (1971) allows computers to become much smaller –Intel chips 4004, 8008, 8086, 80286, etc. Personal (home) computing –Applications for non-specialists Intense competition Internet only used in large companies, universities
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1990s & 2000s Computer for communication and mass medium Internet as a virtual library & soapbox Tech companies (Apple, Microsoft, Intel, Nokia,…) mature and gain clout Growing need to manage information
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Binary Numbers Binary = “base 2” The “2” means each bit is either 0 or 1 To interpret a binary number, use place value system.
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Place value system In base 10, what does 278 mean? 278 = 2 * 10 2 + 7 * 10 1 + 8 * 10 0 Each digit corresponds to a power of 10
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Binary example So now let’s try base 2: What is 11010? 1 * 2 4 + 1 * 2 3 + 0 * 2 2 + 1 * 2 1 + 0 * 2 0 More concise to simply say 2 4 + 2 3 + 2 1
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Powers of 2 2 0 = 1 2 1 = 2 2 2 = 4 2 3 = 8 2 4 = 16 2 5 = 32 2 10 ~ 1 thousand 2 20 ~ 1 million 2 30 ~ 1 billion 2 40 ~ 1 trillion
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Binary Decimal In a binary number, each “1” gives you a power of 2 More examples: 11 101 110 1110
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Questions Let’s say we have 4 bits. What is the lowest number? What is the highest number? Try same experiment with 5 bits.
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