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.