1 chapter 1 introduction. 2 objective computer science 可以把它當成是一門與電腦相...

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Chapter 1 Introduction

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Objective

Computer Science 可以把它當成是一門與電腦相關的學科。為了要瞭解電腦的運作，我們把電腦想像成一個黑盒子，想要嘗試去瞭解電腦共通的特徵，例如電腦中一定要有那一些元件，分別負責甚麼功能，好像在做模型一樣。

這個電腦共通的模型，稱為 von Neumann model。這個章節我們就要先瞭解甚麼是 von Neumann model，並在後面的章節中一一再詳述所有的概念。

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Outlines

The Computer as a Black Box Von Neumann Model Computer Hardware Data Computer Software History Key Terms Summary Practice Set Homework

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Section 1.1The Computer as a Black Box

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Computer as a Black box

Computer science as “issues related to the computer”

Look a computer as a black box How to define the job performed by this box? Two common computer model:

• Data processor• Programmable data processor

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Data Processor Model

ComputerInput Data

Output Data

A computer acts as a black box • Accept input data• Process the data• Create output data

Disadvantage: • It is too general.• It does not specify the type of processing.

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Programmable Data Processor Model

ComputerInput Data

Output Data

Program

A program is a set of instructions that tells the computer what to do with data.

A program is a set of instructions written in a computer language.

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Example: C Language

#include <iostream>using namespace std;main( ) { int a=0,b=0,c=0 ; /* variable declaration */ cin >> a; /* read input */ cin >> b; c=a+b; /* variable operation */ cout << c ; /* output to screen */}

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Same Program, Different Data

ComputerInput Data

14, 6, 8, 12

Output Data

6, 8, 12, 14

Sort Program

ComputerInput Data

3, 12, 8, 22

Output Data

3, 8, 12, 22

Sort Program

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Same Data, Different Program

ComputerInput Data

3, 12, 8, 22

Output Data

3, 8, 12, 22

Sort Program

ComputerInput Data

3, 12, 8, 22

Output Data

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Add Program

ComputerInput Data

3, 12, 8, 22

Output Data

3

SmallestProgram

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Same Program, Same Data

ComputerInput Data

3, 12, 8, 22

Output Data

3, 8, 12, 22

Sort Program

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Comparison of Two Models

Data processor• It represents a specific-purpose computer.• Sometime, we call it as processor.

Programmable data processor• Computers are general-purpose machines.

In Section 1.2, we will try to use von Neumann model to find:

How does a general-purpose computer work?

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Section 1.2Von Neumann Model

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Von Neumann Model

Every computer today is based on the von Neumann model.• John von Neumann

Basic on three ideas:• Four subsystems• Stored program concept• Sequential execution of instructions

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Four Subsystems (1/2)

Memory: storage area Arithmetic Logic Unit (ALU): perform

arithmetic and logic operations Input/Output (I/O): accept input data and

send output data Control Unit: control the operations of the

memory, ALU and I/O.

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Four Subsystems (2/2)

Input Data

Output Data

Program

Control Unit

Arithmetic Logic Unit

Memory

Input/Output

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Stored Program Concept

Both the data and programs stored in memory.

Program and data should have the same format because they are stored in the same memory.

Program

Data

memory

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Sequential Execution of Instructions

A program is made of a finite number of instructions.

The instructions are executed one after another.

The control unit • Fetches one instruction from memory • Interpret it (decode) • Execute it

Fetch

Execu

te

Decode

Instruction Cycle

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Real Computer

Von Neumann model is just a model! How to realize a computer? There are 3 components in a computer:

• Computer Hardware in Section 1.3• Computer Software (Program) in Section 1.5• Data in Section 1.4

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Section 1.3Computer Hardware

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Computer Hardware

A physical computer must contains all components in von Neumann model.

We will discuss computer hardware in Chapter 5.

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Computer Network

How to communicate 2 computers? See Chapter 6

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Section 1.4Data

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Storing Data (1/2)

How to store data in memory? Computer processing is performed by electronic

devices, which are switches with only two possible states: on and off.• If the electrical signal is in a storage device

(presence), it is assigned a value of 1 and it is on. • If the electrical signal is not in a storage device

(absence), it is assigned a value of 0 and it is off. • Two states (binary: 0/1)

Storage is a binary world!

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Storing Data (2/2)

How to store different types of data as a binary pattern? • Ex: 2 v.s. 00000010 in 2’ complement• Ex: 4 v.s. 00000100 in 2’ complement• Ex: 100 v.s. 01100100 in 2’ complement

How data are manipulated as a binary pattern?• Ex: Binary addition / subtraction / logical operation• Ex: 2+2=4 v.s. 010+010=100

Answers are in Chapters 2,3,4.

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Data Organization

Data outside a computer can take many forms.

Data is stored in binary form inside a computer.• Data are organized into small units. • Small units organized into larger units.

Answers are in Chapters 11-14: data structure, abstract data structure, file structure, database.

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Section 1.5Computer Software

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Computer System

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Programming

The main feature of the von Neumann model is the concept of the stored program.

Two aspects of programming:• A sequence of instructions• Programs must be stored (into the memory when

they run!)

See Chapter 9

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Program and Data in Memory

Memory is used to hold data and program.

Program

Data

Program

main memory

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Program Made in Instructions

cin >> A; cin >> B; C=A+B; cout << C;

Program to find the summation of two integer

Why a program must be made of instruction? Answer is reusability.

• Basic instructions are provided by computer hardware.

• Programmers combine these instructions to perform thousand of tasks.

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Algorithm

How to write a program by a programmer? 1. Solve the problem in a step-by-step manner.

2. Try to find the appropriate instructions and combine them as a program

The step-by-step solution is called an algorithm. (See Chapter 8)

1. Input first data item into memory. (call it as A) 2. Input second data item B into memory. (call it as B) 3. Add the two together and store the result in memory. 4. Output the result. Algorithm to find the summation of two integer

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Computer Languages

Machine language: 0 and 1 only! Computer language: the idea of using

symbols to represent binary patterns• Ex: C language, Java

Compare to Natural language:• Computer language has more limited number of

symbols, and a limited number of words.• Ex: Summary/Addition v.s. +• Ex: read from standard input v.s. cin >>• Ex: print out to standard output v.s. cout <<

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Software Engineering

Software engineering is the design and writing of structured programs.

The program must follow strict principles and rules.• Ex: True is 1, False is 0.• Ex: Analysis → Design → Prototype → Test → A

large scale product• Ex: Full documents

See Chapter 10.

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System Development

Define SystemSpecification

Develop Real

System

Create Prototype

Use Prototype

Modify Prototype

User OK?

User suggestion

yes

no

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Operating System (OS)

There are a series of instructions (tasks) common to all programs. It is not necessary to write the same tasks in all programs.• Ex: receive data from keyboard

The operating system originally worked as a manager to facilitate access of the computer components for a program.• Ex: Windows, Unix, FreeBSD

See Chapter 7.

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Advanced Topics

Chapter 15: data compression Chapter 16: security Chapter 17: theory of computation

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Data Compression

MPEG framesRun-Length

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Security

Public Key Encryption

Secret Key Encryption

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Theory of Computation

Turing Machine

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Section 1.6History

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The History of Computing and Computer

There are three periods: Mechanical machines (before 1930) Birth of electronic computer (1930-1950)

• Early electronic computers• Computers based on von Neumann model

Computer generations (1950-present)• First to Fifth generations

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The Advances of Hardware in Computer

Mechanical (1896) Mechanical + Electrical (1930) Vacuum Tube (1944) Transistors (1959) Integrated Circuit (IC) (1967) Storages (CD-ROM, DVD)

vacuum tube

transistorIC

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Mechanical Machines

Abacus Based on the technology of gears

• Blaise Pascal (1623-1662) • Gottfriedn Wilhelm Lebniz (1646-1716)• Joseph-Marie Jacquard’s loom (1801) • Charles Babbage (1792-1871)

Difference EngineAnalytic Engine: all components in von Neumann modelAugustra Ada Byron: First Programmer in the world

• Herman Hollerith (1860-1929)Automatic read/write data from/to punched cards

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Pascal’s Machine

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Jacquard Loom

The first machine used the idea of store and programming!

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Babbage’s Machines

Analytical Engine

Difference Engle

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Birth of Electronic Computers (1/2)

Electronic mechanical machine• Howard Aiken & IBM’s Maker I (1930s)

Digital computer with vacuum tube• John Atanasoff & Clifford Berry’s Atanasoff-Berry

Machine: ABC, first special-purpose electrical computer (1939)

• 1946, ENIAC, first general-purpose electronic computer

• Konrad Zuse’s Z1 (about 1939)• Alan Turing’s COLOSSOS

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Birth of Electronic Computers (2/2)

Above machines:• Memory only for storing data• Programmed externally by using wires or switch

The first computer based on von Neumann model is Pennsylvania’s EDVAC (1950).

At the same time, Cambridge’s EDSAC is created by Maurice Wilkes.

After 1950, almost computers are following the von Neumann model.

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Mark I

Begin at 1937, Finished at 1944 Leader: Howard Aiken

• Work with IBM• Idea come from Babbage

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The Mark I Computer, completed in 1940 at Harvard University

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ENIAC

“ Where... the ENIAC is equipped with 18,000 vacuum tubes and weighs 30 tons, computers in the future may have 1,000 vacuum tubes and perhaps weigh just 1-1/2 tons.” Popular Mechanics, March 1949, p.258

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Computer Generations (1950-Present)

First Generation (roughly 1950-1959)• Commercial computers, professionals, Mainframe

Second Generation (roughly 1959-1965)• Transistors, FORTRAN, COBOL

Third Generation (roughly 1965-1975) • Integrated circuit (IC), Minicomputer, software packet

Forth Generation (roughly 1975-1985) • VLSI, Microcomputer, computer network

Fifth Generation (started in 1985)• Laptop, storage, multimedia, virtual reality

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Technology Trends

ProcessingIntegration

• Single-chip systems

Communication• Optical and wireless

Storage density - CDROM, DVD etc

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Market Trend - “Consumer Friendly”

Visual Communication• 3D sounds and images

Internet Explosion• Information and communication

Information Appliances• Personal organizers• Mobile phones• Wearable computers

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A Growing Industry

In 2008, there are 109 desktop computers or notebooks in the world.• The growth rate is about 12%.• In 2014, there are 2×109 PC in the world.

科技產業資訊室• http://cdnet.stpi.org.tw/techroom.htm

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Section 1.7Key Terms

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Key Terms (1/2)

How many terms can you describe?• Algorithm• Arithmetic logic unit (ALU)• Black box• Computer language• Computer Science• Control unit• Data processor• Input data• Instruction• Integrated circuit

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Key Terms (2/2)

How many terms can you describe?• Memory• Microcomputer• Operating system• Output data• Program• Programmable data processor• Software• Software engineering• Von Neumann model

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Section 1.8Summary

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Summary (1/3)

Computer science means issues related to a computer.

A computer is a programmable data processor that accepts input data and programs and outputs data.

A program is a set of instructions executed sequentially that tells the computer what to do with data.

Every computer today is based on the von Neumann model.

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Summary (2/3)

The von Neumann model specifies • A memory subsystem• An arithmetic logic unit subsystem• A control unit subsystem• An input subsystem• An output subsystem

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Summary (3/3)

Data and programs are stored in computer memory.

A step-by-step solution to a problem is called an algorithm.

A program is written in a computer language. Software engineering is the design and

writing of programs in a structured form.

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Practice Set

Review Questions Multiple-Choice Questions Exercises

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Homework

Review Questions: 5,6,7,8,9,11 Multiple-Choice Questions: 12-26 Exercises: 32, 33