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Introduction to Computer Science
Unit 5
• Basic Elements of Java
• A Look at Hardware and
Software
What this Course is Not
• This is not a course on Java, even
though we spend time learning this
language
• It’s a course introducing Computer
Science, which also means introducing
programming (principles are better
understood when they are concrete)
• Java is a means to what we want to
accomplish, not an end in itself
5- 2
Course Mission Statement
“To give the student the tools to
develop correct, efficient, wellstructured, and stylish programs,
and to build a foundation for further
studies in Computer Science.”
-An Introduction to Computer Science with Java
Kamin, Mickunas, and Reingold
5- 3
Why We Like Java
• Java is Object Oriented to the core
• Java is, in certain key ways,
simpler than other Object Oriented
languages (like C++)
• Java is well-suited to the Internet
• Java is cross-platform
• Java’s popularity creates its own
momentum
5- 4
A Simple Program
• A Java application:
class Hello {
public static void main (String[ ] args) {
// Say hello.
System.out.println(“Hello!”);
}
}
5- 5
The Way You’ll Type It (sometimes
I’ll do it this way, too)
• A Java application:
import intro2cs.utils.*;
class Hello {
public static void main (String[ ] args) {
// Say hello.
System.out.println(“Hello!”);
WaitKey.waitKey();
}
}
5- 6
Take it Apart
import some classes
import intro2cs.utils.*;
class heading
class Hello {
method heading
public static void main (String[ ] args) {
// Say hello.comment
System.out.println(“Hello!”);
print out “Hello!”
WaitKey.waitKey();
} wait for user to press key
} before finishing
5- 7
Java Cares About File Names
• Type the program into a file named
Hello.java (case matters)
• Java demands that the class name
(here, “Hello”) must also be the base
name of the file into which you put it
• The extension of the file must be .java
• Hence, Hello.java
• Each Class Requires a Separate File
5- 8
Steps to Nirvana
• Type the program into a file named
Hello.java (case matters; really)
• Compile it
• Execute it
• The program displays the message
Hello!
on the screen
5- 9
Compilation
• Many high-level languages, like C, Pascal, or C++,
must be compiled before they are run
• Compilation means translation into the native
language of the computer
• Each computer (Wintel, Macintosh, Sun Sparc,
etc.) has its own native language, so compiling
the same program for each computer would
create something different
• The statement “x = 3 + 2;” would be translated
into a sequence of low-level operations
5- 10
Compilation
C, Pascal, or C++ program
Source code
Compilation
1001110110101101
1101110001011010
Machine code
for some
specific
machine
5- 11
Interpretation
• Other languages, like Lisp and SmallTalk, are
interpreted
• They don’t get translated directly into machine
language
• Instead, they are given to an interpreter, which is
a program that performs each operation in the
program on the computer
• The statement “x = 3 + 2;” would cause some
sequence of operations to be carried out
5- 12
Interpretation
Lisp or SmallTalk program
Source code
Read by an
Interpreter
Lisp or SmallTalk
Interpreter for a
Specific Machine
Machine code for
some specific
machine
5- 13
Some Differences
• Compilation and Interpretation differ in many ways
• When machine code is generated/activated
– At compile time with compilation
– At run-time with interpretation
• The kind of machine code that is
generated/activated
– Compilation can do optimizations
• The flexibility of development
– Interpreters are more flexible because you don’t have to
recompile when you make changes to a program
5- 14
Where does Java fit?
• Compilation is efficient, but machinespecific
• Interpretation is flexible, but inefficient
• Java wanted to be efficient, but also
flexible, and most important:
PLATFORM INDEPENDENT (same
program running on all computers)
• So Java is compiled and interpreted...
5- 15
Compilation and Interpretation
• A Java program can basically
exist in one of two states:
–Source code (that’s what you are
typing in)
–Byte code (a translation of the
original code to something closer to
the machine’s language --- but not
any real machine’s language)
5- 16
Compilation and Execution
class Hello {
public static void main...
Source code
Compilation
op7 op342 op213 op431
Byte code
Execution
Interpreter
5- 17
Java Byte Code
5- 18
The Java Virtual Machine
• The Java Virtual Machine is the
interpreter that reads Java byte codes
and carries out real machine operations
• To get Java running on any kind of
computer, just implement the Java
Virtual Machine
• Presto! Java is platform independent,
and flexible (interpreted), but still
reasonably efficient (because Java byte
code is close to machine code)
5- 19
Another Program
(this one takes input)
• We want a program that will do the
following:
Please type the temperature (deg C):
20
20 deg C is 68.0 deg F
5- 20
What the Robot World Lacked
• When we programmed the robot
world, we had no real variables,
and no real input or output
• In Java (as in virtually all
programming languages),
variables are essential
• Each variable has a type
5- 21
Input/Output in Java
import intro2cs.utils.*;
class Temperature {
public static void main (String[ ] args) {
int temperature; // The Celsius temperature
SimpleInput sinp = new SimpleInput(System.in);
System.out.print(“Please type the temperature (deg C): ”);
temperature = sinp.readInt();
System.out.print(temperature);
System.out.print(“ deg C is “);
System.out.print(((9.0 * temperature)/5.0 ) + 32.0);
System.out.println(“ deg F”);
WaitKey.waitKey();
}
}
5- 22
Perceiving Structure
import intro2cs.utils.*;
class Temperature {
public static void main (String[ ] args) {
int temperature; // The Celsius temperature
SimpleInput sinp = new SimpleInput(System.in);
System.out.print(“Please type the temperature (deg C): ”);
temperature = sinp.readInt();
System.out.print(temperature);
System.out.print(“ deg C is “);
System.out.print(((9.0 * temperature)/5.0 ) + 32.0);
System.out.println(“ deg F”);
WaitKey.waitKey();
}
}
5- 23
Helping Perceive Structure
import intro2cs.utils.*;
class Temperature {
public static void main (String[ ] args) {
int temperature;
// The Celsius temperature
SimpleInput sinp = new SimpleInput(System.in);
System.out.print(“Please type the temperature (deg C):”);
temperature = sinp.readInt();
System.out.print(temperature);
System.out.print(“ deg C is ”);
System.out.print(((9.0 * temperature)/5.0 ) + 32.0);
System.out.println(“ deg F”);
WaitKey.waitKey();
}
}
5- 24
Variables
class Temperature {
public static void main (String[ ] args) {
int temperature;
// The Celsius temperature
• temperature is a variable
• The declaration of the variable
int temperature;
saves a space for a value to be stored later,
but doesn’t store anything there
• The assignment to the variable
temperature = sinp.readInt();
actually puts something in the space that was
created by the declaration
5- 25
Variable Declaration
class Temperature {
public static void main (String[ ] args) {
int temperature;
// The Celsius temperature
temperature
You don’t know what’s in there;
don’t use temperature yet
5- 26
Simple Variable Assignment
temperature = 36;
36
36
temperature
Puts the integer 36 into temperature;
now you can use temperature
5- 27
You Can Combine the Two
Steps
class Temperature {
public static void main (String[ ] args) {
int temperature = 36; // The Celsius temperature
36
temperature
5- 28
What the Program Looked Like
import intro2cs.utils.*;
class Temperature {
public static void main (String[ ] args) {
int temperature;
// The Celsius temperature
SimpleInput sinp = new SimpleInput(System.in);
System.out.print(“Please type the temperature (deg C):”);
temperature = sinp.readInt();
System.out.print(temperature);
System.out.print(“ deg C is ”);
System.out.print(((9.0 * temperature)/5.0 ) + 32.0);
System.out.println(“ deg F”);
WaitKey.waitKey();
}
}
5- 29
Variable Assignment
SimpleInput sinp = new SimpleInput(System.in);
temperature = sinp.readInt();
readInt()
20
20
sinp
temperature
Create new object called sinp (from SimpleInput
class); Send the object sinp a readInt() message, it
returns an integer, which is then placed in temperature
5- 30
Special Variables
that Remain Constant
• We can define a variable (a “symbolic
constant”) whose value will never change,
by writing
final int RETIREMENT_AGE = 70;
• This carries out assignment at the same
time as declaration (as we can do with any
variable)
• Now RETIREMENT_AGE cannot be legally
changed in the program
5- 31
Data Types and Expressions
• Different kinds of information
• Each kind is a “type”
• Java has many data types
–Each type has a name
–Each type has a set of literals
–Each type has a set of operations
• Data types in Java can be
simple types or object types
5- 32
Different Simple Types in Java
• int
–represents integers
–literals like 3 and 132
–operators like + , - , * , /
• double
–represents real numbers
–literals like 3.0, 3.14159 and 2.997925e8
• The integer 3 and the double 3.0 are
represented differently inside the computer
5- 33
More Simple Types in Java
• boolean
–Represents true and false
• char
–Represents individual characters
that are typed at the keyboard
5- 34
Expressions
• An Expression represents a value that can
be used in Java statements
– Made out of literals, variables, symbolic
constants, and operations
– Every expression also has a type
– 3 + 4 + temperature
(has type int)
– (3.0 / 4.0)* RETIREMENT_AGE (has type double)
• Use parentheses to establish the order of
operations
• Can also be messages sent to an object, like
sinp.readInt( )
5- 35
Type of an Expression
No matter how simple or
complicated an
expression is, it always
has a Java type, just
like a variable.
5- 36
Where’s the Expression Go?
• An expression produces a value,
which is then often used in an
assignment statement
• So typically, the expression is on the
right hand side of the assignment
statement:
– temperature = 36;
– temperature = (x / 7) + y;
– temperature = sinp.readInt( );
5- 37
The Order of Assignment
• In general, the computer evaluates the
expression on the right side, and
places that value in the variable on the
left side, replacing the old value. So:
temperature = temperature + 10;
is completely legal; it adds 10 to the
value of temperature
5- 38
Increment/Decrement
• Two special cases: incrementing
and decrementing
cent++;
is the same as
cent = cent + 1;
cent--;
is the same as
cent = cent - 1;
5- 39
One of Your Own Kind,
Stick to Your Own Kind
• Java is very strict about data types and
assignments
• Java only puts into a variable a value of
the appropriate type
• Expressions having an integer value
can go into an integer variable, etc.
• You can’t do this:
int i;
double x = 3.0;
i = 10.3 * x;
5- 40
Exceptions
• You can assign an integer
expression to a double variable
–The integer is converted to a double
without loss of information, so it is
done automatically
• You can do this:
int i = 3;
double x;
x = 10 * i;
5- 41
Converting Values from One
Type to Another
• The cast operation lets you explicitly
convert one type to another
• You can do this:
int i;
double x = 3.0;
i = (int) (10.3 * x);
• The cast (int) takes the expression that
follows it and converts it into an integer by
removing any fractional part; i is assigned
the integer value 30
5- 42
Object Types in Java
• The existence of a class in Java lets you have
variables that are of new types, rather than just
simple types
• (Java gives us simple types int, double,
boolean, char, etc.)
• Every class C defines a set of values called
objects of type C (that is, C is a class name)
• Just as you define a new variable to be of type
int, you can define a new variable (object) to be
of type C
5- 43
Defining Objects of Type C
C u, v, w;
Object type
declares u, v, and w to be objects of type
C (or “variables of type C” or “instances
of type C”)
• This is similar to writing
Simple type
int a, b, c;
to declare a, b, and c to be variables of
type int
5- 44
One of these things,
Is not like the other
• If C and D are two different classes,
their objects have different types
• They can’t be assigned to one another
• If we have
D t; // an object of type D
we cannot do either of the following:
u = t;
t = u;
• We also can’t do something like
u = 10;
5- 45
Constructors
• Declaring a new object just tells the
system the type of the object:
C u;
• To create the object, we use a
constructor:
u = new C( arguments );
• A constructor is a special method of
the class that initializes the new object;
it has the same name as the class
• It is the only way to create objects
5- 46
Creating Objects and Filling
them with Values
• This looks a lot like how we created
objects in the robot world
• Yes, the two statements (declaration and
creation) can be combined:
C u = new C( arguments );
• That’s all we were doing in the robot
world --- combining declaration (declaring
the type of the object) with constructing a
new object.
5- 47
They Look the Same
But They are Different
C u = new C( arguments );
• The first C and the second C fulfill two different
roles
• The first C tells the type of the object variable
(like int tells the type of a simple variable)
• The second C is a call to the method C inside the
class C that is the class’ constructor, and
creates the object
5- 48
Methods within an Object
• If u is an object of class C, and
class C has a method called
“display”, then we’ll apply a method
to u by writing:
u.display( arguments )
• You’ve already seen the same thing
in the robot world
• We’re sending the object u a
message “display” with arguments
5- 49
You can also send messages to
Classes
• Unlike in the robot world, there
are cases when a class is sent a
message, rather than an object
• We saw this when we sent the
waitKey( ) message to the WaitKey
class in our sample programs
• Later we’ll talk about when we do
this kind of thing
5- 50
The String Class
• This is an important predefined,
special class that we are given as
part of the Java system
• Can be used as follows:
String t1 = “To be ”,
t2 = “or not to be.”;
System.out.print(t1 + t2);
prints out: To be or not to be.
5- 51
The String Class
has some useful Methods
• Strings have a method called "length":
String t1 = “To be ”,
t2 = “or not to be.”;
• t1.length( ) then is an expression that
returns the integer 6, the number of
characters in the object t1
• We send the object t1 a message length( ),
and get back the integer 6; we are asking
the object about itself; that’s common
5- 52
Fun with Strings and +
System.out.print(“4” + “5”);
System.out.print(“4” + 5);
System.out.print(4 + 5);
System.out.print(“4” + “005”);
System.out.print(“4” + 005);
System.out.print(“4” * 5);
//prints: 45
//prints: 45
//prints: 9
//prints: 4005
//prints: 45
//error!
• An integer concatenated to a string is
automatically converted to a string
5- 53
Statements
• We’ve seen two Java programs that are
sequences of statements, each statement
either assigning a value to a variable, or an
executable statement that prints output
System.out.print(“Please type the temperature (deg C): ”);
temperature = sinp.readInt();
• There are of course other kinds of
statements, conditionals (if, if/else), and
iterative statements (like loop and while)
5- 54
Perceiving Structure (Again)
import intro2cs.utils.*;
class Temperature {
public static void main (String[ ] args) {
int temperature; // The Celsius temperature
SimpleInput sinp = new SimpleInput(System.in);
System.out.print(“Please type the temperature (deg C): ”);
temperature = sinp.readInt();
System.out.print(temperature);
System.out.print(“ deg C is “);
System.out.print(((9.0 * temperature)/5.0 ) + 32.0);
System.out.println(“ deg F”);
WaitKey.waitKey();
}
}
5- 55
Debugging a Program
We're going to walk
through a
debugging of a
sample program
5- 56
Write and Debug a Program
• Compute the total cost of a coffee order
• ( (Price per pound) x Weight ) + Shipping
• Shipping =
((Shipping Rate per pound) x Weight ) +
Fixed handling fee
• Price per pound and Weight vary
• Shipping Rate per pound and handling
fee are fixed
5- 57
import intro2cs.utils.*;
class CoffeeOrder {
public static void main (String[ ] args) {
final int
RATE_PER_POUND = 1.25,
FIXED_FEE,
int
priceperPound, weight,
shippingCost, coffeeCost;
SimpleInput sinp = new SimpleInput(System.in);
System.out.println(“Enter price per pound: );
pricePerPound = sinp.readInt();
System.out.print(“Enter number of pounds: “);
weight = sinp.readInt();
shipingCost = RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = priceperPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shipingCost);
System.out.println(“Total cost is “ totalPrice);
}
}
import intro2cs.utils.*;
class CoffeeOrder {
public static void main (String[ ] args) {
final int
RATE_PER_POUND = 1.25,
FIXED_FEE,
int
priceperPound, weight,
shippingCost, coffeeCost;
ERROR
SimpleInput sinp = new SimpleInput(System.in);
System.out.println(“Enter price per pound: );
pricePerPound = sinp.readInt();
ERROR
System.out.print(“Enter number of pounds: “);
weight = sinp.readInt();
shipingCost = RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = priceperPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shipingCost);
System.out.println(“Total cost is “ totalPrice);
}
}
import intro2cs.utils.*;
class CoffeeOrder {
public static void main (String[ ] args) {
final int
RATE_PER_POUND = 1.25,
FIXED_FEE;
int
priceperPound, weight,
shippingCost, coffeeCost;
SimpleInput sinp = new SimpleInput(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sinp.readInt();
System.out.print(“Enter number of pounds: “);
weight = sinp.readInt();
shipingCost = RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = priceperPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shipingCost);
System.out.println(“Total cost is “ totalPrice);
}
}
import intro2cs.utils.*;
class CoffeeOrder {
public static void main (String[ ] args) {
final int
RATE_PER_POUND = 1.25,
FIXED_FEE;
int
priceperPound, weight,
shippingCost, coffeeCost;
SimpleInput sinp = new SimpleInput(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sinp.readInt();
System.out.print(“Enter number of pounds: “);
weight = sinp.readInt();
shipingCost = RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = priceperPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shipingCost);
System.out.println(“Total cost is “ totalPrice);
}
}
ERROR
import intro2cs.utils.*;
class CoffeeOrder {
public static void main (String[ ] args) {
final int
RATE_PER_POUND = 1.25,
FIXED_FEE;
int
priceperPound, weight,
shippingCost, coffeeCost;
SimpleInput sinp = new SimpleInput(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sinp.readInt();
System.out.print(“Enter number of pounds: “);
weight = sinp.readInt();
shipingCost = RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = priceperPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shipingCost);
System.out.println(“Total cost is “ + totalPrice);
}
}
import intro2cs.utils.*;
class CoffeeOrder {
public static void main (String[ ] args) {
final int
RATE_PER_POUND = 1.25,
ERROR FIXED_FEE;
int
priceperPound, weight,
shippingCost, coffeeCost;
SimpleInput sinp = new SimpleInput(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sinp.readInt();
ERRORSystem.out.print(“Enter number of pounds: “); ERROR
weight = sinp.readInt();
shipingCost = RATE_PER_POUND+weight +FIXED_FEE;
ERRORtotalPrice = priceperPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
ERRORSystem.out.println(“Shipping cost is “ + shipingCost);
System.out.println(“Total cost is “ + totalPrice);
}
ERROR
ERROR
ERROR
}
ERROR ERROR
import intro2cs.utils.*;
class CoffeeOrder {
public static void main (String[ ] args) {
final double RATE_PER_POUND = 1.25,
FIXED_FEE = 1.95;
int
pricePerPound, weight,
shippingCost, coffeeCost, totalPrice;
SimpleInput sinp = new SimpleInput(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sinp.readInt();
System.out.print(“Enter number of pounds: “);
weight = sinp.readInt();
shippingCost=RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = pricePerPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shippingCost);
System.out.println(“Total cost is “ + totalPrice);
}
}
import intro2cs.utils.*;
class CoffeeOrder {
public static void main (String[ ] args) {
final double RATE_PER_POUND = 1.25,
FIXED_FEE = 1.95;
int
pricePerPound, weight,
shippingCost, coffeeCost, totalPrice;
SimpleInput sinp = new SimpleInput(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sinp.readInt();
ERRORSystem.out.print(“Enter number of pounds: “);
weight = sinp.readInt();
shippingCost=RATE_PER_POUND+weight +FIXED_FEE;
totalPrice = pricePerPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shippingCost);
System.out.println(“Total cost is “ + totalPrice);
}
ERROR
}
import intro2cs.utils.*;
class CoffeeOrder {
public static void main (String[ ] args) {
final double RATE_PER_POUND = 1.25,
FIXED_FEE = 1.95;
double
pricePerPound, weight,
shippingCost, coffeeCost, totalPrice;
SimpleInput sinp = new SimpleInput(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sinp.readInt();
System.out.print(“Enter number of pounds: “);
weight = sinp.readInt();
shippingCost=RATE_PER_POUND+weight +FIXED_FEE;
coffeeCost = pricePerPound * weight;
totalPrice = pricePerPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shippingCost);
System.out.println(“Total cost is “ + totalPrice);
}
}
We run the program
Enter price per pound: 8.95
java.lang.NumberFormatException: 8.95
at java.lang.Integer.parseInt(Integer.java)
at java.lang.Integer.<init>(Integer.java)
at sinp.readInt…
at CoffeeOrder.main(CoffeeOrder.java…
We’ve got a problem. We tried to read a double
by sending sinp the readInt() message.
5- 67
import intro2cs.utils.*;
class CoffeeOrder {
public static void main (String[ ] args) {
final double RATE_PER_POUND = 1.25,
FIXED_FEE = 1.95;
double
pricePerPound, weight,
shippingCost, coffeeCost, totalPrice;
SimpleInput sinp = new SimpleInput(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sinp.readDouble();
System.out.print(“Enter number of pounds: “);
weight = sinp.readInt();
shippingCost=RATE_PER_POUND+weight +FIXED_FEE;
coffeeCost = pricePerPound * weight;
totalPrice = pricePerPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shippingCost);
System.out.println(“Total cost is “ + totalPrice);
}
}
We Run the Program Again
Enter price per pound: 8.95
Enter number of pounds: 3
Coffee total is 26.849999999999998
Shipping cost is 6.2
Total cost is 33.05
Great!
Only one problem. The total cost is $0.50 too high.
5- 69
import intro2cs.utils.*;
class CoffeeOrder {
public static void main (String[ ] args) {
final double RATE_PER_POUND = 1.25,
FIXED_FEE = 1.95;
double
pricePerPound, weight,
shippingCost, coffeeCost, totalPrice;
SimpleInput sinp = new SimpleInput(System.in);
System.out.println(“Enter price per pound: “);
pricePerPound = sinp.readDouble();
System.out.print(“Enter number of pounds: “);
weight = sinp.readInt();
shippingCost=RATE_PER_POUND*weight +FIXED_FEE;
coffeeCost = pricePerPound * weight;
totalPrice = pricePerPound * weight + shippingCost;
System.out.println(“Coffee total is “ + coffeeCost);
System.out.println(“Shipping cost is “ + shippingCost);
System.out.println(“Total cost is “ + totalPrice);
}
}
We Run the Program One Last
Time
Enter price per pound: 8.95
Enter number of pounds: 3
Coffee total is 26.849999999999998
Shipping cost is 5.7
Total cost is 32.55
That’s good enough for now.
5- 71
Transparent vs. Opaque
Functionality
• There used to be a visible
connection between physical
things and what they did
–a butter churn
–a loom
–a watch
• The coming of electrical power
changed all that
5- 72
The Computer
• The computer is the supreme example
of opaque function
• Looking into the box does not help us
to understand what is going on
• The best way to understand
computers is to understand the logical
layers out of which they are built
5- 73
The Layers of Computing
Application
Layer
Software
Browser Compiler Games
Utilities
System
Layer
Software
UNIX
Windows
Apple
System
Machine
Layer
Software
Assembly
Languages
Machine
Languages
MicroPrograms
Underlying
hardware
Memory
Screen
CPU
Hard disk
Keyboard
5- 74
The "Classic" Computer
Architecture
Screen - Output
Hard disk
CPU
Memory
Keyboard - Input
5- 75
The "Classic" Typewriter
Architecture
Paper - Output
Direct Mechanical Action
Keyboard - Input
5- 76
What Makes the Computer
Different?
• Memory
–Short-term
–Long-term
• Programmable
–Multi-purpose
• Communication-enabled
5- 77
ASCC Mark I, "Automatic
Sequence-Controlled Calculator"
• Built at Harvard by Howard Aiken, completed
January 1943
• Approaching architecture of a modern computer
• Used mechanical electromagnetic relays for
storing numbers and doing calculations
• The machine was 51 feet long, weighed 5 tons,
and incorporated 750,000 parts. It included 72
accumulators
• 1947: Aiken predicts that the United States will
need a total of six electronic digital computers
5- 78
ENIAC, the first electronic
computer
• Eckert and Mauchly, University of
Pennsylvania, November 1945
• ENIAC's architecture resembles that of the
Harvard Mark I, but its components are
entirely electronic, incorporating 17,468
vacuum tubes
• The machine weighs 30 tons, covers about
1000 square feet of floor, and consumes
130 kilowatts of electricity; it uses vacuum
tubes
5- 79
ENIAC
• The machine incorporates 20
accumulators (the original plan
was for 4). Each accumulator
stores a 10-digit number, using 10
bits to represent each digit
• A separate unit can perform
multiplication (in about 3
milliseconds), while another does
division and square roots
5- 80
ENIAC
• A card reader is available to input
data values, and there is a card
punch for output
• The program is set up on a
plugboard --- this is considered
reasonable since the same or
similar program would generally be
used for weeks at a time
• The ENIAC's clock speed is 100 kHz
5- 81
ENIAC
5- 82
More ENIAC
5- 83
EDVAC, "Electronic Discrete
Variable Automatic Computer"
EDVAC was the first stored program computer
Oppenheimer and von Neumann
5- 84
EDSAC, Electronic Delay
Storage Automatic Computer
• Based on EDVAC report, first full-scale
operational stored program computer,
May 1949
• 16 tanks of mercury give a total of 256 35bit words (or 512 17-bit words).
• The clock speed of the EDSAC is 500 kHz;
most instructions take about 1500 ms to
execute.
• Its I/O is by paper tape, and a set of
constant registers is provided for booting
5- 85
Lots More History
• Brattain, Bardeen, and Shockley
invent the transistor, which eventually
replaces vacuum tubes, Dec. 1947
• Noyce invents the integrated circuit,
which puts multiple connected
transistors onto a chip, January 1959
• Hoff invents programmable computer
on a chip, Intel 4004, 1970
5- 86
Inventor of Intel 4004 Computeron-a-Chip, Marcian Hoff
5- 87
Intel 4004
•
•
•
•
2250 transistors on the chip
Processed 4 bits of data at a time
600,000 operations a second
Followed by (in Intel's line of chips)
–the Intel 8008
–the 8080, the first chip that made a
personal computer possible
–the 8088, and the 8086, and the 80286,
80386, 80486, Pentium, Pentium II, III, IV ...
5- 88
Underlying Hardware—CPU
• Central Processing Unit (CPU) — speed measured
using many different benchmarks
– Integer performance, SPECint*_base2000
– Floating point performance, SPECfp*_base2000
– Entertainment benchmarks, internet benchmarks, …
• Pentium, Pentium II, III, IV, PowerPC, Sun Sparc
• See, for example,
http://www.intel.com/performance/resources/desktop/index.htm for
information about Pentium IV performance
5- 89
Underlying Hardware—RAM
• Random Access Memory (RAM) — size
measured in megabytes, or millions of bytes
• Holds programs while they are being run
• A byte is 8 bits (binary digits), representing
(roughly) one character
• 2002 desktop computer might have from 256
to 1024 megabytes of RAM; more powerful
computers can have much more RAM
5- 90
Underlying Hardware—Hard Disk
• Hard disk holds programs “permanently”
(even while power is off)
• 2002 desktop computer might have
between 40 to 120 gigabytes of hard disk
storage
5- 91
Underlying Hardware—
Removable Media
• Floppy disks, writeable CDs (CD-R) and DVDs (DVD-R,
DVD+R, DVD-RW, DVD+RW) and tape allow data to be
backed up or transfered from one computer to another
• 2002 desktop computer works with removable diskettes
that hold 1.44 megabytes of data
• Growing popularity of Zip drives, 1 gigabyte Jaz drives
(Iomega), flash memory up to 128MB or 256MB are
common (MemoryStick, CompactFlash, Secure Digital,
MultiMediaCard), …
5- 92
Underlying Hardware—
Input/Output Devices
• Input devices, like a keyboard and a
mouse (and a microphone, and a joystick,
and a trackball, and a pen, and a scanner,
and…)
• Output devices, like a screen and a
printer (and a speaker, and a plotter, and a
laser printer, and…)
5- 93
A Brief Diversion
• Doug Engelbart, the inventor of the mouse
(and windowed interfaces, and more):
http://www2.bootstrap.org/history.htm
•The first mouse:
5- 94
Input Devices that didn't take
off
• The chord key set:
5- 95
Names you probably don't
know
• Short History of the Internet
http://www.umr.edu/~dunaw/net-history.html
• Paul Baran, of the RAND Corporation,
commissioned by the U.S. Air Force to do a
study on how it could maintain its
command and control over its missiles and
bombers, after a nuclear attack. Suggested
a packet-switched network.
http://www.umr.edu/~dunaw/net-history.html
• Leonard Kleinrock, UCLA researcher who
connects computer to switch to another
computer, 2 September 1969
• Ray Tomlinson, BBN engineer who invents
email in 1972, "a quick hack", chooses the
@ http://www.pretext.com/mar98/features/story2.htm
5- 96
Typical Desktop Hardware
Configuration, 2002
•
•
•
•
•
•
•
Pentium IV processor, running at 2.0 GHz
512 MB of RAM
Flat Screen LCD 15” color monitor
Built-in ethernet and modem
CD-RW, DVD drives
60 gigabyte hard disk
Approximate cost in U.S.: $1300
5- 97
Typical Desktop Hardware
Configuration, 1984
• IBM AT 80286 processor, running
at 6 MHz
• 256 KB of RAM, expandable to
3MB using five expansion cards
• Monochrome monitor (color
graphics card)
• 20 MB hard disk
• Approximate cost in U.S.: $6600
5- 98
Hardware Comparison, 1984 –2002
• IBM AT 80286
processor, running at
6 MHz
• 256 KB of RAM,
expandable to 3MB
using five expansion
cards
• Monochrome monitor
(color graphics card)
• 20 MB hard disk
• Approximate cost in
U.S.:
$6600
• Pentium IV processor, running
at 2.0 GHz
• 512 MB of RAM
• Flat Screen LCD 15” color
monitor
• Built-in ethernet and modem
• CD-RW, DVD drives
• 60 gigabyte hard disk
• Approx. cost in U.S.: $1300
Price/performance ratio
improvement, factor of over 4000
5- 99
The Meaning of
Exponential Growth
• Moore’s Law: the computing power available at a
fixed price will double every 18 months
• This has been true for over the last 35 years, and
will continue to be true in coming years
• Most people cannot grasp the real meaning of
exponential growth, confusing it with linear
growth at a sharp angle over the short term
5- 100
Exponential Growth, Doubling
Every 18 months, 1974 = 1, 2001 = 262144
Exponential Growth
70000
60000
50000
40000
30000
20000
1998
1995
1992
1989
1986
1983
1980
1977
0
1974
10000
Year
5- 101
If Cars Improved the Way
Computers Do
• A Rolls Royce would cost $1 and travel
5000 kilometers on a liter of gasoline
• But it would be too small to get into
• Really:
–$20,000 in 1967
–$5,000 in 1970
–$1,250 in 1973
–$0.0025 in 2002
5- 102
Why We Don’t Notice It
4
3.5
3
2.5
2
1.5
1
0.5
0
1995
1998
We are focused on short periods, where the difference
between linear and exponential is obscured
5- 103
Exponential Growth, Doubling
Every 18 months, 1974 = 1, 2001 = 262144
Exponential Growth
70000
60000
50000
40000
30000
20000
1998
1995
1992
1989
1986
1983
1980
1977
0
1974
10000
Year
5- 104
But the Future is Just as Amazing
1200
1000
800
600
400
200
0
1995
1995 = 1
1998
2001
1998 = 4
2004
2007
2010
2010 = 1024
5- 105
Two Curves
powerful
weak
then
The Hardware Curve
now
then
The Software Curve
now
powerful
weak
5- 106
Two Major Developments
• The two biggest developments in the
computer industry in the last 5 years:
–The transition of the computer from a
computing device to a communications
and computing device
–The ever-shrinking, ever-cheaper
computing power has led to “computers
everywhere”, digital appliances,
embedded and standalone
5- 107
Where Does it End?
• By 2012, the layer thickness of integrated circuits will
measure just less than one nanometer, equivalent to
five silicon atoms
• Two papers by Harvard and Cornell researchers in the
June 13, 2002 issue of the journal Nature described a
breakthrough in miniaturization: researchers have
created transistors whose switching components are
literally single atoms (but they lack “gain” and work
just at very low temperatures).
• What happens when the physical limits are reached?
Does the hardware curve straighten out? Do new
technologies (optical computing, DNA computing,
quantum computing) provide new solutions?
5- 108
The Layers of Computing
Application
Layer
Software
Browser Compiler Games
Utilities
System
Layer
Software
UNIX
Windows
Apple
System
Machine
Layer
Software
Assembly
Languages
Machine
Languages
MicroPrograms
Underlying
hardware
Memory
Screen
CPU
Hard disk
Keyboard
5- 109
Machine Layer Software
• Machine language instructions—
built into the computer, a
language of 1’s and 0’s
• Assembly language instructions—
use brief English-like mnemonics
that carry out slightly more
complicated instructions.
Assembly language is directly and
easily translatable into machine
language, using an assembler
5- 110
Machine Layer Software (II)
• Nowadays, there is less of a distinction
between machine language and
assembly language
• Computers are built that have “built-in”
translators
• Microcode—a machine language
program built into the CPU—is run
when an assembly language command
is given. So the assembly language is
the machine language!
5- 111
The Layers of Computing
Application
Layer
Software
Browser Compiler Games
Utilities
System
Layer
Software
UNIX
Windows
Apple
System
Machine
Layer
Software
Assembly
Languages
Machine
Languages
MicroPrograms
Underlying
hardware
CPU
Memory Hard disk Keyboard
5- 112
System Layer Software
• The machine layer software is very
low level—we need a second layer
of software to take care of details
• The operating system is a
constantly running program that:
–keeps track of computer resources
–seems to be controlling the computer
5- 113
System Layer Software—
the Operating System
• The operating system:
–“Listens” to keyboard and mouse for input
–“Talks” to screen and printer
–Interprets commands as they are input
–Makes programs available to the user and lets
him install new ones
–Stores information in files, and manages them
–Controls access to the computer
–Splits CPU’s attention between several jobs
–Communicating with other computers
5- 114
Lots of Operating Systems
• But there are three most popular ones
today:
UNIX (and its Linux variant)
Windows (‘98, NT, XP)
Apple Macintosh OS X (built on top of Unix)
• They differ in big and small ways—
timesharing, graphical interface, power…
• Also, embedded systems and handhelds
5- 115
What’s the Connection?
• Question: What’s the relationship between
an operating system and hardware?
• Answer: Not much, even though each
operating system has a “most common”
implementation on particular hardware:
–Windows on 80x86 chips, but Windows NT on
others
–Macintosh on 680x0 chips and PowerPC chips
–UNIX on SPARC chips, but also on 80x86 chips
and 680x0 chips…and others
5- 116
What’s a GUI?
• A Graphical User Interface is
commonplace in computing these days
• The Apple Macintosh has it, machines
with Microsoft Windows have it, the
Xerox Star had it, Unix machines have
it (in many flavors)
• A graphical interface contrasts with a
character-based interface, such as MSDOS or plain Unix gives you
5- 117
Graphical User Interface
• The GUI runs on top of the
Operating System, and makes the
Operating System easier to use
• Usually includes: bitmapped
displays, menus, windows, use of
a pointing device (like a mouse),
buttons, etc.
5- 118
Windows XP
5- 119
The Layers of Computing
Application
Layer
Software
Browser Compiler Games
Utilities
System
Layer
Software
UNIX
Windows
Apple
System
Machine
Layer
Software
Assembly
Languages
Machine
Languages
MicroPrograms
Underlying
hardware
CPU
Memory Hard disk Keyboard
5- 120
Application Layer Software
• These are the programs that do
specific jobs—word processors,
drawing programs, spreadsheet,
tax programs, etc.
Applications
• Applications are written in
Programming Language
any convenient language—
Pascal, C, Lisp, Modula-2,
Operating System
Ada, Fortran…
• The underlying platform is usually
a specific operating system
5- 121
Programming Languages
• Low level (first or second
generation languages) are closely
tied to the computer’s instruction
set. They are good when:
–the program must control some
hardware that can only be controlled
in this low-level language
–the program must run extremely
quickly
5- 122
Higher-level Languages
• Higher level languages (third
generation languages) like Pascal, C,
C++, Java, etc. are more disconnected
from the hardware on which they run
• They can be used to solve any kind of
problem
• They can run on any kind of computer
5- 123
Java
• Designed by Sun team led by James
Gosling
• Originally called Oak, it was intended for
consumer devices like TV-top boxes
• Being cross platform, and more stable
than C++, were essential goals
• When the TV-top market didn’t
materialize, figured they’d try the internet
5- 124
Fourth Generation Languages
• Application languages (fourth
generation) are more high level
languages, but also more specialized
• Examples are PostScript, database
languages, etc.
• They are very good at the tasks they
do, and clumsy for general-purpose
tasks
5- 125
Some PostScript Code
%!PS-Adobe-3.0 EPSF-2.0
%%Creator: Windows PSCRIPT
%%Title: PowerPoint - UNIT5.PPT
%%BoundingBox: 13 10 577 832
%%DocumentNeededResources: (atend)
%%DocumentSuppliedResources: (atend)
%%Pages: 0
%%BeginResource: procset Win35Dict 3 1
/Win35Dict 290 dict def Win35Dict begin/bd{bind def}bind def/in{72
mul}bd/ed{exch def}bd/ld{load def}bd/tr/translate ld/gs/gsave ld/gr
/grestore ld/M/moveto ld/L/lineto ld/rmt/rmoveto ld/rlt/rlineto ld
/rct/rcurveto ld/st/stroke ld/n/newpath ld/sm/setmatrix ld/cm/currentmatrix
ld/cp/closepath ld/ARC/arcn ld/TR{65536 div}bd/lj/setlinejoin ld/lc
/setlinecap ld/ml/setmiterlimit ld/sl/setlinewidth ld/scignore false
def/sc{scignore{pop pop pop}{0 index 2 index eq 2 index 4 index eq
and{pop pop 255 div setgray}{3{255 div 3 1 roll}repeat setrgbcolor}ifelse}ifelse}bd
/FC{bR bG bB sc}bd/fC{/bB ed/bG ed/bR ed}bd/HC{hR hG hB sc}bd/hC{
5- 126
The Field of Computer Science
• We’ve been looking at computers
(software and hardware), but
that’s not an accurate description
of the field of Computer Science:
Hardware
Software
Theory
5- 127
Areas in Computer Science
•
•
•
•
•
•
•
•
•
•
Algorithms and Data Structures
Programming Languages
Computer Architecture
Operating Systems
Software Engineering
Symbolic and numerical computation and
modeling, graphics
Databases
Artificial Intelligence
Robotics
Computer Vision
5- 128
How they fit together
Hardware
Architecture
Software
Theory
Languages
Algorithms
Software
Engineering
Operating
Systems
Databases
Robotics
Symbolic/Numerical
Computation
Artificial Intelligence
5- 129