Why invent the computer? IS112 Fall 2005. What did people need a computer? Difficult problems for people to solve by hand Minimize or eliminate mistakes.

Why invent the computer?

IS112 Fall 2005

What did people need a computer? Difficult problems for people to solve by hand Minimize or eliminate mistakes and errors Even today, problems known as

Grand Challenges exist that can’t be solved with existing computers

NSF funds projects using High Performance Computing and Communication (HPCC)

Military and computers

For the past 300 hundred years, governments such as France, England, and the United States have worked towards producing a computer

Accurate calculations are essential for the military

Can you think of why that is?

Military and computation

How does accurate calculation help with ship navigation? Ship determine their location when out at sea

using angles and trigonometry Why does the military need accurate

calculations for ballistics (the study of an object in motion) Must to be able to accurately aim cannons and

missiles at a target

Trigonometric tables

Navigation and ballistics depend on accurate trigonometric values such as sin, cosine, and tangent Trig Table

The first comprehensive calculation and publication of trigonometric values by the French Royal Academy of Sciences (1801), resulted in 17 volumes (i.e. individual books) 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 (Eniac) During WW II the army wanted to improve accuracy of cannons

(so they would hit the desired target) Apply ballistics –the study of objects in motion

Formula includes many factors: initial angle, wind speed, force of gravity, and others

Army wanted trajectory tables – i.e. information that they could use to aim their cannons and more reliable hit the desired target

Eniac calculated trajectory tables

First Computer - Eniac

Weighed 30 tons, 1800 sq. ft., dimmed lights of Philadelphia when turned on

Photo1 Photo2 Program that created

trajectory tables was “hard wired” into Eniac

“Re-programming” required taking machine apart and re-connecting different components

Stored Program Concept

Eniac could only do one job – produce trajectory tables But there are other uses for computers, how did they make them

more flexible? Solution: add hardware (CPU) to could carry out instructions Add memory (RAM) to load and make available the required

instructions, in order to allow the CPU to access them one by one

Stored instructions called “program” Instructions are written in a programming language

The modern computer

All computers now store programs that are executing in memory Modern software consists of a series of instructions that are

execute one by one by the CPU We will be studying a simple example of a stored program

machine – the Lobo Simulator You will write instructions that will be stored in memory Then you will see the CPU execute those instructions one at a

time

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

Summary

Creating a computer has been a goal for centuries

For many reasons, accurate calculations are needed for both military and commerce

The first working electronic computer (Eniac) only could execute one program – generate trajectory tables

Summary – cont.

Modern computers are designed to be able to execute a variety of programs

What parts allow them to do this? Memory – the instructions to be executed are stored

in memory, and are grabbed (“fetched”) by the CPU one at a time

CPU – the processor, the brain of the computer, carries out each instruction it encounters