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 * 102
+ 7 * 101
+ 8 * 100
• Each digit corresponds to a power of 10
Binary example• So now let’s try base 2: What is 11010?
1 * 24 + 1 * 23 +
0 * 22 +
1 * 21 +
0 * 20
• More concise to simply say24 + 23 + 21
Powers of 2
• 20 = 1
• 21 = 2
• 22 = 4
• 23 = 8
• 24 = 16
• 25 = 32
• 210 ~ 1 thousand
• 220 ~ 1 million
• 230 ~ 1 billion
• 240 ~ 1 trillion
Binary Decimal
• In a binary number, each “1” gives you a power of 2
• More examples:
11
101
110
1110
Questions
• Let’s say we have 4 bits.
• What is the lowest number?
• What is the highest number?
• Try same experiment with 5 bits.