CS 4, Summer 2006: Lecture 1: Introduction & History

Welcome

Your perspective?

• What is a computer?
• What is computer science?
• Why do you care?

Some thoughts

• Brian Kernighan: universality
  • Numbers are a universal representation (music, pictures, books)
  • Computers are universal number processors
  • The internet is a universal number carrier
  • Universal gadgets: cell phone = computer with radio, iPod = computer with headphones, ...
• Sean Smith: A liberal arts education centers on thinking and knowledge. CS is the study of the physical embodiments of thinking and knowledge.
• General consensus: Fun! Freedom! Creativity! Make things happen that otherwise just couldn't! Learn to communicate a process precisely!
• Invitation to Computer Science (ICS): some misconceptions about CS
  • not just about the machines (just like biology is not just about the microscopes), but also what can we do with them
  • not just about programming, but also about the stuff leading up to it (analysis and design) and following it (testing)
  • not just about applications (just like automotive engineering is not about driving cars)
  Also a precise definition of what it is, centered on the idea of an "algorithm", or step-by-step method for accomplishing a task.

What we'll cover

(see also the schedule page)

• How do we represent information?
• How do we compute with those representations?
• How do we make a program do those computations?
• How does a computer carry out that program?
• What can a computer do and not do?
• What can we do with computers?

Administrative stuff

See http://www.cs.dartmouth.edu/~cbk/4/ for

• News
• Who, when, where
• Requirements: homeworks, exams
• Policies: follow the honor code
• HW 0: apply for web space now
• Schedule

A brief history of computing machines

To see some historical computing machines used at Dartmouth over the years, and learn about their history (teaser: one exhibit is "when computers were human"), visit the Count on It exhibit at the Kresge/Cook Library. Take a friend!

Calculation: mechanical

Abacus, circa 3000 B.C.: addition, subtraction, multiplication, division

• Information stored in positions of beads.
  

Blaise Pascal's "Pasacline", 1642 (he was 18): addition

• Information stored in positions of gears.
• Upon cranking, rods and meshing gears transferred information.
  

Gottfried Wilhem von Leibniz, 1694: extended Pascal's design to include multiplication.

Charles Xavier Thomas de Colmar, 1820: invented the arithometer that could add, subtract, multiply and divide.

Programmable: punch cards

Joseph Jacquard (1752-1834): punch card loom

• Holes punched in a card controlled movement of the warp strings.
• Cards described patterns and the looms cycled through the cards.
• Encoded knowledge of master weaver, for automation.
• Software piracy: competing manufacturers would steal card decks.
  

Charles Babbage (1792-1871): Difference Engine (1820s)

• Could perform many arbitrary sequences of arithmetic, in some cases to as many as 31 digits of precision.
• The Kensington Science Museum built a replica of the Difference Engine in the 1990s.
  

Babbage, with Lady Ada Lovelace: designed (but never completed) first general purpose computer -- the steam-powered Analytical Engine.

• Included 50,000 components, input device (perforated cards) containing instructions, memory (1,000 numbers), a control unit that allowed instructions to be processed in any order, and an output device.
• Lady Lovelace (daughter of the poet Lord Byron) helped develop a "program" for computing a sequence of Bernoulli numbers.

Herman Hollerith (1860-1929): 1890 census via punch card tabulator.

• Estimates said it would take 8 to 9 years by hand; machine helped do it in 6 weeks.
• Tiny wires detected the presence or absence of holes.
• His company eventually became known as IBM.
  

Let's get digital

Mark I, 1945 ($200,000): sines, cosines, logs, and basic arithmetic.

• Harvard's Howard Aiken (1900-1973) helped design it after finding a model of Babbage's difference engine sitting in an attic.
• 51 feet long, 8 feet high and 2 feet wide; over 10,000 pounds.
• About 5 operations per second.
  

ENIAC, 1944: artillery shell trajectories

• Roughly 18000 vacuum tubes, weighed 30 tons, dimmed lights in section of Philadelphia.
• Up to 5000 additions per second.
  

The CPU

• John von Neumann (1903-1957) simplified the model.
• One "central processing unit" would do the calculation.
• The program would be stored in memory and fed into the CPU to tell it what to do.
• No need to replug wires or rewire the machine; no more wiring "bugs".
  
• But the word "bug" stuck. Grace Hopper started using it to refer to correcting ("debugging") programs.
• Beginning of software.

Quotes about where computers are heading:

"I think there is a world market for maybe five computers."
   --Thomas Watson, IBM chairman, 1943

"Computers in the future may weigh no more than 1.5 tons."
   --Popular Mechanics, 1949

The modern era

Transistor (1956): replace vacuum tubes; smaller, faster, more reliable

• IBM Stretch: 50,000 ops/sec, $3.5 million
  

Programming languages (1960s): COBOL, FORTRAN, LISP

• High-level languages make it easier and faster to program computers; "compilers" convert to machine-understandable code.
• At Dartmouth, John Kemeny and Thomas Kurtz invented BASIC.
• Somewhat later, a man by the name of Bill Gates got his start making BASIC available for an early personal computer.

Integrated circuits (1960s): multiple transistors per chip

• 100,000+ ops/sec.
• "There is no reason anyone would want a computer in their home."   --Ken Olson, president, chairman and founder of Digital Equipment Corp., 1977

Personal computers (1970s): Apple, Commodore, Radio Shack

• 1,000,000+ ops/sec.
• 1981: IBM PC
  1984: Macintosh (Mac 1984 commercial)
  

Where are we now?

CS to automobile industry: if we made cars,

• They would cost $1.
• They would go 20,000 mph
• They would get 1,000,000 miles per gallon.

(ICS, p. 28, analogous rate of change from 1909 Model T)

Automobile industry back: but,

• They would crash twice a day for no reason.
• You would need a new car every time they repainted the lines on the road.
• If it stalled, you would need to open and close the passenger's window three times, twist the radio knob to the left for a quarter turn, turn the air conditioner on full blast, and then it would restart.
• Airbags would ask, "Are you sure?" before proceeding.
• You would press the "start" button to turn it off.

(Folklore from multiple sources.)

Where are we going?

Moore's law: processor complexity doubles every 18-24 months.

Computers getting smarter (AI@50)

Computers everywhere (ubiquitous)