Chapter 1: Computer Systems
Presentation slides for
Java Software Solutions
for AP* Computer Science A
2nd Edition
by John Lewis, William Loftus, and Cara Cocking
Java Software Solutions is published by Addison-Wesley
Presentation slides are copyright 2006 by John Lewis, William Loftus, and Cara Cocking. All rights
reserved.
Instructors using the textbook may use and modify these slides for pedagogical purposes.
*AP is a registered trademark of The College Entrance Examination Board which was not involved in
the production of, and does not endorse, this product.
© 2006 Pearson Education
Computer Systems
We first need to explore the fundamentals of
computer processing
Chapter 1 focuses on:
• components of a computer
• how those components interact
• how computers store and manipulate information
• computer networks
• the Internet and the World Wide Web
• programming and programming languages
• graphic systems
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Hardware and Software
Hardware
• the physical, tangible parts of a computer
• keyboard, monitor, disks, wires, chips, etc.
Software
• programs and data
• a program is a series of instructions
A computer requires both hardware and software
Each is essentially useless without the other
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CPU and Main Memory
Chip that executes
program
Central
commands
Processing
Unit
Intel Pentium 4 or
Sun ultraSPARC III
Processor
Primary storage area
for programs and
data that are in
active use Main
Memory
Synonymous with
RAM
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Secondary Memory Devices
Secondary memory Central Information is moved
devices provide Processing between main memory
long-term storage Unit and secondary memory
as needed
Hard disks
Floppy disks Hard Disk
ZIP disks Main
Writable Memory
CDs
Tapes Floppy Disk
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Input / Output Devices
Monitor I/O devices facilitate user
Central
Processing interaction
Unit
Keyboard
Monitor screen
Keyboard Hard Disk
Mouse Main
Joystick Memory
Bar code scanner
Touch screen Floppy Disk
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Software Categories
Operating System
• controls all machine activities
• provides the user interface to the computer
• manages resources such as the CPU and memory
• Windows XP, Windows 2000, Unix, Linux, Mac OS
Application program
• generic term for any other kind of software
• word processors, missile control systems, games
Most operating systems and application programs
have a graphical user interface (GUI)
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Analog vs. Digital
There are two basic ways to store and manage data:
Analog
• continuous, in direct proportion to the data represented
• music on a record album - a needle rides on ridges in the
grooves that are directly proportional to the voltages sent to
the speaker
Digital
• the information is broken down into pieces, and each piece
is represented separately
• music on a compact disc - the disc stores numbers
representing specific voltage levels sampled at specific
times
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Digital Information
Computers store all information digitally:
• numbers
• text
• graphics and images
• video
• audio
• program instructions
In some way, all information is digitized - broken
down into pieces and represented as numbers
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Representing Text Digitally
For example, every character is stored as a number,
including spaces, digits, and punctuation
Corresponding upper and lower case letters are
separate characters
Hi, Heather.
72 105 44 32 72 101 97 116 104 101 114 46
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Binary Numbers
Once information is digitized, it is represented and
stored in memory using the binary number system
A single binary digit (0 or 1) is called a bit
Devices that store and move information are cheaper
and more reliable if they have to represent only two
states
A single bit can represent two possible states, like a
light bulb that is either on (1) or off (0)
Permutations of bits are used to store values
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Bit Permutations
1 bit 2 bits 3 bits 4 bits
0 00 000 0000 1000
1 01 001 0001 1001
10 010 0010 1010
11 011 0011 1011
100 0100 1100
101 0101 1101
110 0110 1110
111 0111 1111
Each additional bit doubles the number of possible permutations
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Bit Permutations
Each permutation can represent a particular item
There are 2N permutations of N bits
Therefore, N bits are needed to represent 2N unique
items
1 bit ? 21 = 2 items
How many 2 bits ? 22 = 4 items
items can be
represented by
3 bits ? 23 = 8 items
4 bits ? 24 = 16 items
5 bits ? 25 = 32 items
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A Computer Specification
Consider the following specification for a personal
computer:
• 2.8 GHz Pentium 4 Processor
• 512 MB RAM
• 80 GB Hard Disk
• 48x CD-RW / DVD-ROM Combo Drive
• 17” Flat Screen Video Display with 1280 x 1024 resolution
• 56 Kb/s Modem
What does it all mean?
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Memory
9278
Main memory is
9279 divided into many
9280 memory locations (or
9281 cells)
9282
9283 Each memory cell has
9284 a numeric address,
9285 which uniquely
9286 identifies it
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Storing Information
9278 Each memory cell stores
9279 10011010 a set number of bits
(usually 8 bits, or one
9280 byte)
9281
Large values are
9282
stored in consecutive
9283 memory locations
9284
9285
9286
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Storage Capacity
Every memory device has a storage capacity,
indicating the number of bytes it can hold
Capacities are expressed in various units:
Unit Symbol Number of Bytes
kilobyte KB 210 = 1024
megabyte MB 220 (over 1 million)
gigabyte GB 230 (over 1 billion)
terabyte TB 240 (over 1 trillion)
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Memory
Main memory is volatile - stored information is lost if
the electric power is removed
Secondary memory devices are nonvolatile
Main memory and disks are direct access devices -
information can be reached directly
The terms direct access and random access often are
used interchangeably
A magnetic tape is a sequential access device since
its data is arranged in a linear order - you must get by
the intervening data in order to access other
information
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RAM vs. ROM
RAM - Random Access Memory (direct access)
ROM - Read-Only Memory
The terms RAM and main memory are basically
interchangeable
ROM could be a set of memory chips, or a separate
device, such as a CD ROM
Both RAM and ROM are random (direct) access
devices!
RAM probably should be called Read-Write Memory
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Compact Discs
A CD-ROM is portable read-only memory
A microscopic pit on a CD represents a binary 1 and
a smooth area represents a binary 0
A low-intensity laser reflects strongly from a smooth
area and weakly from a pit
A CD-Recordable (CD-R) drive can be used to write
information to a CD once
A CD-Rewritable (CD-RW) can be erased and reused
The speed of a CD drive (48x) describes the
maximum data transfer speed. Writing is typically
much slower than reading.
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DVDs
A DVD is the same size as a CD, but can store much
more information
The format of a DVD stores more bits per square inch
A CD can store 650 MB, while a standard DVD can
store 4.7 GB
• A double sided DVD can store 9.4 GB
• Other advanced techniques can bring the capacity up to 17.0
GB
There are various recordable DVD technologies – the
market will determine which will dominate
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The Central Processing Unit
A CPU is on a chip called a microprocessor
It continuously follows the fetch-decode-execute cycle:
Retrieve an instruction from main memory
fetch
execute decode
Carry out the Determine what the
instruction instruction is
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The Central Processing Unit
The CPU contains:
Performs
Arithmetic / Logic Unit calculations and
makes decisions
Coordinates
Control Unit processing
steps
Small
Registers storage
areas
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The Central Processing Unit
The speed of a CPU is controlled by the system clock
The system clock generates an electronic pulse at
regular intervals
The pulses coordinate the activities of the CPU
The speed is measured in megahertz (MHz)
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Monitor
The size of a monitor (17") is measured diagonally,
like a television screen
Most monitors these days have multimedia
capabilities: text, graphics, video, etc.
A monitor has a certain maximum resolution ,
indicating the number of picture elements, called
pixels, that it can display (such as 1280 by 1024)
High resolution (more pixels) produces sharper
pictures
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Modem
Data transfer devices allow information to be sent
and received between computers
Many computers include a modulator-demodulator or
modem, which allows information to be moved
across a telephone line
A data transfer device has a maximum data transfer
rate
A modem, for instance, may have a data transfer rate
of 56,000 bits per second (bps)
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Networks
A network is two or more computers that are
connected so that data and resources can be shared
Most computers are connected to some kind of
network
Each computer has its own network address, which
uniquely identifies it among the others
A file server is a network computer dedicated to
storing programs and data that are shared among
network users
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Network Connections
Each computer in a network could be directly
connected to every other computer in the network
These are called point-to-point connections
Adding a computer requires
a new communication line
for each computer already
in the network
This technique is not practical for
more than a few close machines
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Network Connections
Most networks share a single communication line
Adding a new computer to the network is relatively
easy
Network traffic must take Often information is broken
turns using the line, which down in parts, called packets,
introduces delays which are sent to the receiving
machine and then reassembled
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Local-Area Networks
A Local-Area Network
(LAN) covers a small
distance and a small
number of computers
LAN
A LAN often connects the machines
in a single room or building
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Wide-Area Networks
A Wide-Area Network (WAN)
connects two or more LANs,
often over long distances
LAN
A LAN usually is owned
by one organization, but
a WAN often connects
groups in different
LAN
countries
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The Internet
The Internet is a WAN which spans the entire planet
The word Internet comes from the term
internetworking, which implies communication among
networks
It started as a United States government project,
sponsored by the Advanced Research Projects Agency
(ARPA) - originally it was called the ARPANET
The Internet grew quickly throughout the 1980s and 90s
Less than 600 computers were connected to the
Internet in 1983; by the year 2000 there were over 10
million
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TCP/IP
A protocol is a set of rules that determine how things
communicate with each other
The software which manages Internet communication
follows a suite of protocols called TCP/IP
The Internet Protocol (IP) determines the format of
the information as it is transferred
The Transmission Control Protocol (TCP) dictates
how messages are reassembled and handles lost
information
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IP and Internet Addresses
Each computer on the Internet has a unique IP
address, such as:
204.192.116.2
Most computers also have a unique Internet name,
which also is referred to as an Internet address:
spencer.villanova.edu
kant.gestalt-llc.com
The first part indicates a particular computer
(spencer)
The rest is the domain name, indicating the
organization (villanova.edu)
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Domain Names
The last part of each domain name, called a top-level
domain (TLD) indicates the type of organization:
edu - educational institution
com - commercial entity
org - non-profit organization
net - network-based organization
Sometimes the suffix
indicates the country: New TLDs have
uk - United Kingdom recently been added:
au - Australia
ca - Canada biz, info, tv, name
se - Sweden
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Domain Names
A domain name can have several parts
Unique domain names mean that multiple sites can
have individual computers with the same local name
When used, an Internet address is translated to an IP
address by software called the Domain Name System
(DNS)
There is no one-to-one correspondence between the
sections of an IP address and the sections of an
Internet address
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The World Wide Web
The World Wide Web allows many different types of
information to be accessed using a common
interface
A browser is a program which accesses and presents
information
• text, graphics, video, sound, audio, executable programs
A Web document usually contains links to other Web
documents, creating a hypermedia environment
The term Web comes from the fact that information is
not organized in a linear fashion
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The World Wide Web
Web documents are often defined using the
HyperText Markup Language (HTML)
Information on the Web is found using a Uniform
Resource Locator (URL):
http://www.lycos.com
http://www.villanova.edu/webinfo/domains.html
ftp://java.sun.com/applets/animation.zip
A URL indicates a protocol (http), a domain, and
possibly specific documents
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Problem Solving
The purpose of writing a program is to solve a
problem
The general steps in problem solving are:
• Understand the problem
• Dissect the problem into manageable pieces
• Design a solution
• Consider alternatives to the solution and refine it
• Implement the solution
• Test the solution and fix any problems that exist
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Problem Solving
Many software projects fail because the developer
didn't really understand the problem to be solved
We must avoid assumptions and clarify ambiguities
As problems and their solutions become larger, we
must organize our development into manageable
pieces
This technique is fundamental to software
development
We will dissect our solutions into pieces called classes
and objects, taking an object-oriented approach
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Java
A programming language specifies the words and
symbols that we can use to write a program
A programming language employs a set of rules that
dictate how the words and symbols can be put
together to form valid program statements
The Java programming language was created by Sun
Microsystems, Inc.
It was introduced in 1995 and it's popularity has
grown quickly since
It is an object-oriented language
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Java Program Structure
In the Java programming language:
• A program is made up of one or more classes
• A class contains one or more methods
• A method contains program statements
These terms will be explored in detail throughout the
course
A Java application always contains a method called
main
See Lincoln.java (page 27)
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Java Program Structure
// comments about the class
public class MyProgram
{
class header
class body
Comments can be placed almost anywhere
}
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Java Program Structure
// comments about the class
public class MyProgram
{
// comments about the method
public static void main (String[] args)
{
method header
method body
}
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Comments
Comments in a program are called inline documentation
They should be included to explain the purpose of the program
and describe processing steps
They do not affect how a program works
Java comments can take three forms:
// this comment runs to the end of the line
/* this comment runs to the terminating
symbol, even across line breaks */
/** this is a javadoc comment */
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Identifiers
Identifiers are the words a programmer uses in a
program
An identifier can be made up of letters, digits, the
underscore character ( _ ), and the dollar sign
Identifiers cannot begin with a digit
Java is case sensitive - Total, total, and TOTAL
are different identifiers
By convention, Java programmers use different case
styles for different types of identifiers, such as
• title case for class names - Lincoln
• upper case for constants - MAXIMUM
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Identifiers
Sometimes we choose identifiers ourselves when
writing a program (such as Lincoln)
Sometimes we are using another programmer's code,
so we use the identifiers that they chose (such as
println)
Often we use special identifiers called reserved
words that already have a predefined meaning in the
language
A reserved word cannot be used in any other way
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Reserved Words
The Java reserved words:
abstract else interface super
assert enum long switch
boolean extends native synchronized
break false new this
byte final null throw
case finally package throws
catch float private transient
char for protected true
class goto public try
const if return void
continue implements short volatile
default import static while
do instanceof strictfp
double int
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White Space
Spaces, blank lines, and tabs are called white space
White space is used to separate words and symbols
in a program
Extra white space is ignored
A valid Java program can be formatted in many ways
Programs should be formatted to enhance
readability, using consistent indentation
See Lincoln2.java (page 33)
See Lincoln3.java (page 34)
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Language Levels
There are four programming language levels:
• machine language
• assembly language
• high-level language
• fourth-generation language
Each type of CPU has its own specific machine
language
The other levels were created to make it easier for a
human being to read and write programs
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Programming Languages
A program must be translated into machine language
before it can be executed on a particular type of CPU
This can be accomplished in several ways
A compiler is a software tool which translates source
code into a specific target language
Often, that target language is the machine language
for a particular CPU type
The Java approach is somewhat different
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Java Translation
The Java compiler translates Java source code into a
special representation called bytecode
Java bytecode is not the machine language for any
traditional CPU
Another software tool, called an interpreter,
translates bytecode into machine language and
executes it
Therefore the Java compiler is not tied to any
particular machine
Java is considered to be architecture-neutral
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Java Translation
Java source
code Java
bytecode
Java
compiler
Java Bytecode
interpreter compiler
Machine
code
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Development Environments
There are many environments for developing Java
software:
• Sun Java Development Kit (JDK)
• Sun NetBeans
• Borland JBuilder
• MetroWerks CodeWarrior
• Microsoft Visual J++
• IBM Eclipse
• Monash BlueJ
Though the details of these environments differ, the
basic compilation and execution process is
essentially the same
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Syntax and Semantics
The syntax rules of a language define how we can
put together symbols, reserved words, and identifiers
to make a valid program
The semantics of a program statement define what
that statement means (its purpose or role in a
program)
A program that is syntactically correct is not
necessarily logically (semantically) correct
A program will always do what we tell it to do, not
what we meant to tell it to do
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Errors
A program can have three types of errors
The compiler will find syntax errors and other basic
problems (compile-time errors)
• If compile-time errors exist, an executable version of the
program is not created
A problem can occur during program execution, such
as trying to divide by zero, which causes a program
to terminate abnormally (run-time errors)
A program may run, but produce incorrect results,
perhaps using an incorrect formula (logical errors)
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Basic Program Development
Edit and
save program
errors
errors
Compile program
Execute program and
evaluate results
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Introduction to Graphics
The last one or two sections of each chapter of the
textbook focus on graphical issues
Most computer programs have graphical
components
A picture or drawing must be digitized for storage on
a computer
A picture consists of pixels, and each pixel is stored
separately
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Representing Color
A black and white picture can be stored using one bit
per pixel (0 = white and 1 = black)
A colored picture requires more information; there
are several techniques for representing colors
For example, every color can be represented as a
mixture of the three additive primary colors Red,
Green, and Blue
In Java, each color is represented by three numbers
between 0 and 255 that collectively are called an RGB
value
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Coordinate Systems
Each pixel can be identified using a two-dimensional
coordinate system
When referring to a pixel in a Java program, we use a
coordinate system with the origin in the top-left
corner
(0, 0) 112 X
40
(112, 40)
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Summary
Chapter 1 has focused on:
• components of a computer
• how those components interact
• how computers store and manipulate information
• computer networks
• the Internet and the World Wide Web
• programming and programming languages
• graphic systems
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