Transcript Introduction

Introduction to Computers and Programming
 Hardware
 Software
 Computer languages
 Compiling, interpreting and assembling
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Computer Basics
 A computer system consists of both hardware and software.
 Hardware - the physical components
 Software - the instructions, or rather, computer programs, that
tell the hardware what to do
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Common Hardware Components
Memory
Input
Devices
Output
Devices
Processor
(CPU)
(such as mouse and
keyboard)
 Processor:
(such as video
display or printer)
 Input devices:
 Central Processing Unit (CPU)
 keyboard, mouse, touch-screen
 interprets and executes
program instructions
 game controllers
 Memory:
 sensors
 Output device(s)
 volatile and non-volatile
 video display, printer
 holds data and instructions
 robotic devices
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Classification of Memory
At a high-level there are two types of memory:
 Volatile – contents are lost when power is turned off:
 Main memory (stores programs and data during execution)
 Cache memory
 Fastest and most expensive form of memory, per byte
 Non-Volatile – contents are maintained when power is turned off:
 Hard drive (internal or external, stores programs and data permanently)
 CD, DVD
 Flash drive, floppy disk
 Tape (still used extensively)
 Slowest and cheapest form of memory, per byte
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Memory Organization
 Bit = one binary digit, either 0 or 1
 Byte = 8 bits
 Word = machine dependant, typically 4 bytes
 Larger groupings: (number of bytes)
name
approximation
exact
Kilobyte (KB)
2^10
10^3
Megabyte (MB)
2^20
10^6
Gigabyte (GB)
2^30
10^9
Terabytes (TB)
2^40
10^12
Petabyte (PB)
2^50
10^15
Exabyte (EB)
2^60
10^18
Zetabyte (ZB)
2^70
10^21
Yottabyte (YB)
2^80
10^24
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Binary Encodings
 Everything in memory is “encoded” in binary, i.e., as a sequence
of bits.
“A”
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“DOG”
=>
=>
=>
1000001
101101
01000100 01001111 01000111
 Generally, the encoding of an object is unique among all similar
objects, e.g., the encoding of “A” is different from the encoding of “B.”
 How many binary sequences are there on n bits?
 How many bits are needed to uniquely encode k items?
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Main Memory Organization
 Main memory:
 A list of locations, each
containing one byte of data.
 Each location has an associated
“number,” which is commonly
referred to as its’ address.
 Is said to be byte addressable.
 Also called Random Access
Memory (RAM).
 The number of bytes per data
item may vary from one item to
another, and from one computer
system to another.
 Integer => 4 bytes (1 word)
 Character => 1 or 2 bytes
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Address
Contents
3021
1111 0000
3022
1100 1100
3023
1010 1010
Item 2 (1 byte)
3024
1100 1110
Item 3 (3 bytes)
3025
0011 0001
3026
1110 0001
3027
0110 0011
3028
1010 0010
3029
…
Item 1 (2 bytes)
Item 4 (2 bytes)
Next Item, etc.
Running (Executing) a Program
 A (computer) program is a set of instructions for a computer to follow, or
rather, execute.
 The term application is sometimes used to informally refer to a
computer program (we will use the term more formally later).
Program
Data
(input for the
program)
Output
Computer
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Many Types of Programs
 System Software - Part of the computers “infrastructure,” and necessary
for the system to operate:
 Operating Systems - DOS, Microsoft Windows, MacOS, Linux, UNIX, etc.
 Database Systems – Oracle, IBM DB2, SQL Server, Access
 Networking Software
 Web Servers
 Application Servers
 User Applications - Not required for the system to operate:
 Games
 Office Applications – Word, Powerpoint, Excel
 Web Browsers
 Text Editors – textedit, vi, emacs, notepad
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Various Types of User Interfaces
 Graphical User Interface (GUI)




Windows, menus, buttons, sliders, etc.
MacOS, Windows
Sometimes also called “event-driven” interfaces
First developed by Xerox Corporation
 Command-Line:
 User types in commands one line at a time
 DOS (Start -> run -> cmd)
 Unix xterm
 Application Program Interface (API)
 Allows one program to communication, interact or “interface” with another,
or with some external, physical device.
 ODBC, JDBC, Swing, AWT
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Programming Language Hierarchy
 Programs are written, or coded, in a programming language.
 There are many different types of programming languages.
High-Level Language
Assembly Language
Machine Language
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High-Level Languages
 High-Level Language (HLL):
 Java, C, C++, C#, COBOL, FORTRAN, BASIC, Lisp, Ada, etc.
 closest to natural language
 words, numbers, and math symbols
 multi-line statements/commands
 relatively easy for people to read (it’s for people)
 not directly understood by hardware
 “portable” (hardware independent)
 A program in a HLL is frequently referred to as:
 a source program
 source code
 source file
 source
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High-Level Language Example (Java)
public class SimpleProgram
{
public static void main(String[] args)
{
System.out.println(“Hello out there.”);
System.out.println(“I will add two numbers for you.”);
int x;
double d;
x = 3752;
d = 3.14156;
System.out.println(“The sum of ” + x + “ and ” + d + “ is:”);
System.out.println(x + d);
}
}
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Machine Languages
 Machine Language (lowest level):
 just 0s and 1s
 single-line commands
 very difficult for humans to read
 directly understood by hardware
 not portable (hardware dependent)
 A program in machine language is frequently referred to as:
 an object program
 object code
 executable program
 executable code
 executable
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Machine Language Example
000000
000001
000010
000110
000000
100000
100011
000011
001000
000000
000001
000100
:
:
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Assembly Languages
 Assembly Language:
 a more readable version of machine language (also for people)
 words, abbreviations, letters and numbers replace 0s and 1s
 single-line statements/commands
 easily translated to machine executable code
 like machine code, not portable (hardware dependent)
 So, if we already have HLLs for people, why do we need assembly
language?
 compilation results in a loss of meaning…sort of
 control over the resulting machine code
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Assembly Language Example
PUSH DX
MOV AH 08
INT 21
CMP AL 30
JB 0203
CMP AL 46
JA 0203
CMP AL 39
JA 021B
MOV AH 02
MOV DL AL
INT 21
SUB AL 30
POP DX
RET
CMP AL 41
JB 0203
MOV AH 02
MOV DL AL
INT 21
SUB AL 37
POP DX
RET
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Getting from Source to Machine Code
 Translating a program in a high-level language to machine code is called
compiling.
 A program that compiles programs is called a compiler.
 A program that translates an assembly language program into machine code is
called an assembler.
 Compilers and assemblers need to know the specific target hardware.
 There is, however, one additional type of translation called interpreting…
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Compilers vs. Assemblers vs. Interpreters
 Compilers and Assemblers:
 translation is a separate user step from execution
 entire source program is translated before execution
 sometimes said to be “off-line,” i.e. not at run time
 Interpreters: (another way to translate source to object code)
 translation is not a separate user step from execution
 translation and execution occur “line at a time”
 sometimes said to be “on-line,” i.e. at run time
 The difference between compiling (or assembling) and interpreting a
computer program, is analogous to the difference between translating a
book, and interpreting a speaker.
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Java Program Translation
 Executing a java program involves both compilation and interpretation.
 Java Program Translation & Execution:
 Step #1: A java program is compiled; this produces a program in byte code.
 Similar to assembly code, but hardware independent.
 Step #2: An interpreter, called the Java Virtual Machine (JVM) translates the
byte code program to hardware-specific machine code, and executes it.
 Execution is done in an interpretive manner
 Question:
 Why not compile directly to machine code, rather than byte code?
 Answer:
 To make a long story short, portability over the internet.
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Java Program Translation Including Linker
 Oh, and, one other part of the translation process is linking…
Java Program
Previously Compiled Helper Programs
Java Compiler
Byte-Code
Program
Byte-Code Interpreter
Machine-Language
Instructions
Class Loader (i.e., Linker)
Computer Execution
of Machine-Language Instructions
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