Computer FundamentalsInstructor: Jun YanThursday (3, 4), N229, South Campus

Lecture2 physical realization of computation---computer

刘玉瑜2015050479

Welcome to the class. This lecture covers the following topics：Physical realization of computation---computer

1.  Why should we learn this course?

In the last lecture, we tried to work out a very simple calculation: 3.14*7.2=?

And it is easy for us to get the right answer 22.608. It is a motivating example, which inspires us to think about how to solve the math problem by using some tools, for example computers. But how do the computers realize computation under instruction?

This question triggers this lecture: physical realization of computation---computers

2.  This course is to teach us physical realization of computation of computers.

We are going to learn physical realization of computation of computers, which is in analog to an idea of a black box and a model provided by Von Neumann.

Input black box output

If we learn it well, then it would be much easier for us to know how a computer works.

3.  Content of this course

Contents includes: number system, binary, logical relations and logical gates

4.  von Neumann architecture

Computer appears to us like a black box. The central question of this course is how to design this black box.

To see how to construct a computer in principle, let us first examine a simple calculation taught at elementary school, which serves as a motivating example.

3.14 * 7.2

3.14

× 7.2

22.608

Seeing from the calculation, we can extract three main ingredients of in our computation:

a)  Multiplication table(Rules)

b)  Control

c)  Blackboard（Paper）

Von Neumann architecture exactly captures the ingredients of computation mentioned above.

5.  Stored program and general-purpose computer

Now we can construct, in principle, a computer based on von Neumann architecture. We still have a problem: for each functionality, for example, phone, mp3, media player, game station, and so on, do we need to carry a specific computer for each of them?

Thanks to Turing, we have a single general-purpose computer to all the jobs! The underlying idea is to treat program as data. Alan Turing invented a Turing machine based on a simple number system –binary, which is a new way to record and use numbers, just using two numbers: zero and one. He said: In principle, this little machine is as powerful as any computers in real world. But computer has its limitation.

6. Number system

--Represent a useful set of numbers, giving every number a unique representation

-In our everyday life, we use decimal, why?

-Ten fingers.

7. Other number system in everyday life

a. Binary (2) b. Octal (8) c. Hexadecimal (16) d.Sexagesimal (60)

8. Binary

--It consists of two digits: 0, 1

Addition Multiplication

0+0=0 0*0=0

0+1=1 0*1=0

1+0=1 1*0=0

1+1=10 1*1=1

Have a try: 11+10=? 101*11=?

11 101

+ 10 * 11

101 101

101

1111

-Why computers use binary?

-Binary system is easy for physical realization.

eg:

--Voltage high/low

--Switch on/off

--Current flow/cut off

--Any other two state systems

Watch a video about binary system.

--Binary is not necessary. So we need to learn logical relations and logical gates

9. Logical relations and logical gates

-treat “1” as “true”, “0” as “false”

-AND 、OR、 NOT

-logical gates to implement AND、OR、NOT

AND OR

A B F A B F

T T T T T T

F T F T F T

T F F F T T

F F F F F F

A B F A B F

0 0 0 0 0 0

0 1 0 0 1 1

1 0 0 1 0 1

1 1 1 1 1 1

The class is over. Thank you!

1 / 5