Why invent the computer? Difficult problems for people to solve by hand Minimize or eliminate mistakes and errors (problems exist that are hard to solve with existing computers Grand Challenges)Grand Challenges

What kinds of problems require intensive calculations? Commerce Military requirements Navigation Trajectory tables

Trigonometric tables Navigation and ballistics both depend on trigonometric values Trig TableTrig Table Intensive project by French Royal Academy of Sciences (1801) resulted in 17 volumes of tables Required an army of “human computers” performing 900 to 1000 additions or subtractions per day over a period of several years

First electronic computer Ballistics is study of objects in motion Depends on many factors: initial angle, wind speed, force of gravity, and others Trajectory tables essential for use of cannons and long guns Eniac calculated trajectory tables

Eniac Photo1 Photo2 Photo1Photo2 Weighed 30 tons, 1800 sq. ft., dimmed Phil. City lights when turned on Solution to trajectory table was “hard wired” into Eniac “Re-programming” required taking machine apart and re-connecting different components

Stored Program Concept Next generation added circuitry to allow instructions to be loaded into machine and used to control execution Stored instructions called “program” Instructions are written in a programming language

How do you give instructions to a computer? Computer has limited instruction set Instructions must be written in computer language Machine code Binary code 0s and 1s Circuits that carry electricity (on or off)

Modern programming First programmers either hard wired the machine or wrote instructions as a series of 0s and 1s Modern solution: programmer writes program in “higher level” language Closer to English, with addition of arithmetic operators and some special symbols Then source code is translated (by another program) into the binary code, into the instructions a computer is capable of executing