CS 101 – Aug. 28 A little history Introduce binary numbers

Before 1940s Only analog machines, moving parts Specific purpose –Adding machines –Tabulators –Sunrise/sunset, celestial General computing only theoretical interest –Alan Turing

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

US Army photo

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

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

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

Binary Numbers Binary = “base 2” The “2” means each bit is either 0 or 1 To interpret a binary number, use place value system.

Place value system In base 10, what does 278 mean? 278 = 2 * * * 10 0 Each digit corresponds to a power of 10

Binary example So now let’s try base 2: What is 11010? 1 * * * * * 2 0 More concise to simply say

Powers of = = = = = = ~ 1 thousand 2 20 ~ 1 million 2 30 ~ 1 billion 2 40 ~ 1 trillion

Binary  Decimal In a binary number, each “1” gives you a power of 2 More examples:

Questions Let’s say we have 4 bits. What is the lowest number? What is the highest number? Try same experiment with 5 bits.