Download - Beginning Snapshots
Beginning Snapshots
Chapter 0
C++ An Introduction to Computing, 3rd ed. 2
Objectives
Give an overview of computer science• Show its breadth
Provide context for computer science concepts• Events from the past
Describe basic components, organization of a computer
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Areas of Computer Science
Algorithms and Data Structures
Architecture
Artificial Intelligence and Robotics
Database and Information Retrieval
Human-Computer Communication
Numerical and Symbolic Computation
Operating Systems
Programming Languages
Software Methodology and Engineering
Social and Professional Context
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Important Concepts in Computer History
The mechanism of arithmetic
The stored program
The graphical user interface
The computer network
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Machines to Do Arithmetic
Early calculators• Abacus 3000 B.C.• Stonehenge 1900 – 1600 B.C• Al-Khowarizm 12th Century• Napier's bones 1612• Slide rule 1630• Pascaline 1642• Leibniz' calculator 1673
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The Stored Program
Jacquard loom 1801
Mechanical Computers• Babbage's Difference Engine 1822• Babbage's Analytical Engine 1833• Ada Augusta 1842
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Electromechanical Computers
Hollerith's tabulating machine 1890
Konrad Zuse 1935-1938
Alan Turing 1937
The Mark I 1944
Atanasoff's ElectronicDigital Computer (ABC) 1936-1939
Grace Hopper 1944
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First-Generation Computers
Vacuum tube computers 1945-1956
ENIAC 1943-1946
John Von Neumann's"First Draft of a Report onthe EDVAC" 1945
First bug in a computer 1945
UNIVAC 1951
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Second Generation Computers
Used transistors 1956-1963
FORTRAN 1957
IBM 7090 1958
LISP
COBOL 1960
ALGOL 60
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Third-Generation ComputersChips and Integrated Circuits 1964-1971The IBM System/360 1964The PDP-8 1965Douglas Englebart: the mouse, Two-D display, editing, hypermedia, 1968PascalKen Thompson: UNIX 1969ARPANET – The beginning of the Internet
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Fourth-Generation Computers
Intel 4004 Chip 1971
Dennis Richie: C 1973
Ethernet
Court rules Atanasoff was legal inventor of first electronic digital computer
Altair, BASIC, Apple 1 1974
Apple II, Cray 1, Apple Corp.Microsoft Corp. 1976
IBM PC 1981
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Fourth-Generation Computers
Bjarne Stroustrup: C++ 1983
Novell announces NetwareTCP/IP
Macintosh 1984
Windows 1985
Intel 386 Chip 1986
Tim Berners—Lee: WWW 1991
Linux 1992
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Fourth-Generation Computers
Pentium chips, Power PC chip1993
MOSAIC, Apple Newton
Netscape Navigator 1.0, Yahoo! 1994Palm computing
James Gosling: JAVA 1995Windows 95, Internet Explorer,Internet goes commercial
Windows 98, Apple's IMAC 1998Microsoft's court case
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Fourth-Generation Computers
Y2K Problem, Powermac G4 1999
Windows 2000 20001 GHZ processors
Mac OS X 2001Windows XP
Quantum Computer 2002
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Graphical User Interface
Command line interface required precise and cryptic commands
Xerox PARK had developed GUI prototype in 1972• Steve Jobs saw it several years later and used
new hardware capabilities to implement
GUI makes computer easy to use
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Network
Defn: Two or more computers connect to exchange resources• Processing power• Storage• Access to a printer• Software resources• Messages
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Network
Time sharing in early 1960s• Users communicate with host computer
ARPANET connected research center computers in 1969• Eventually developed into Internet
Local Area Network hardware and operating systems developed late 1970s
ISPs now affordable, widely available for even home computers
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Computing Systems
Computers have two kinds of components:Hardware – physical devices such as• CPU• memory• storage devices
Software – programs such as• Operating system• applications• utilities
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Hardware: CPU
Central Processing Unit (CPU):• the “brain” of the machine• Circuitry that performs arithmetic and logical ML
statements
CPU measurement • Speed (roughly) in megahertz
(millions of clock-ticks per second)
Examples• Intel Pentium, AMD K6, Motorola PowerPC, Sun
SPARC,
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Storage
Random Access Memory (RAM)• “Main” memory, which is fast, but volatile...• Analogous to a person’s short-term memory.• Many tiny “on-off” switches
• “on” is represented by 1, “off” by 0.
Each switch is called a binary digit, or bit.• 8 bits is called a byte.• 210 bytes =1024 bytes is called a kilobyte (1K)• 220 bytes is called a megabyte (1M).
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Storage
Secondary Memory (Disk):• Stable storage using magnetic or optical
media.• Analogous to a person’s long-term memory.• Slower to access than RAM.
Examples: • floppy disk (measured in kilobytes)• hard disk (measured in gigabytes (230 bytes))• CD-ROM (measured in megabytes), ...
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Input and Output
Input devices• Instructions and data must be encoded in
binary form and transmitted to the CPU
Examples:• keyboard• mouse, trackball, joystick• scanner• audio, video capture boards
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Input and Output
Output devices• Convert data from binary to another form
Examples• monitors, printers• sound, video• robotics control
Communication between CPU and peripheral devices is through ports• Ports communicate via the system bus
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Hardware: the Bus
The Bus:• Connects CPU to other hardware devices.• Analogous to a person’s spinal cord.
Speed measured in megahertz • Like the CPU• Typically much slower than the CPU...• The bottleneck in most of today’s PCs.
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Hardware: CacheAccess speed of RAM • Faster than accessing secondary memory• Still quite slow, relative to the rate at which the CPU
runs.
Solution:• Add a fast cache memory to the CPU• Store recently used instructions and data
Assumption:• These instructions/data were needed recently• They will be needed again in the near future.
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Hardware: Summary
Putting the pieces together:
CPU
Bus
MainMemory
SecondaryMemory
cache
Program storage• Long-term in secondary memory• Loaded into main memory to run• From which the CPU retrieves and executes their statements.
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Software: OS
Operating system (OS)• Loaded from secondary memory into main memory
when the computer is turned on,• Remains in memory until the computer is turned off.
DiskRAMCPUCache
Bus
OS
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Software: OS
OS acts as the “manager” of the system, • Making sure that each hardware device
interacts smoothly with the others.
Provides an interface • Enables user to interact with the computer, • Awaits user input if no application is running.
Examples: MacOS, Windows-95, Windows-NT, UNIX, Linux, Solaris, ...
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Software: Applications
Applications are non-OS programs • Perform some useful task• Including word processors, spreadsheets,
databases, web browsers, C++ compilers
Example C++ compilers/environments: • CodeWarrior (MacOS, Win95, WinNT,
Solaris) • GNU C++ (UNIX, Linux)• Turbo/Borland C++ (Win95, WinNT)• Visual C++ (Win95, WinNT)
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Software: User Programs
Programs that are neither OS programs nor applications are called user programs.
User programs are what you’ll be writing in this course.
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What is Programming?
Computer Program• A sequence of statements that instruct a
computer in how to solve a problem.
Programming• The act of designing, writing and maintaining
a program
Programmers • People who write programs
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What kinds of statementsdo computers understand?
A computer only understands machine language statements.
Characteristics of machine language• A sequence of ones and zeros • Cause the computer to perform a particular
action, such as add, subtract, multiply, ...
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Machine Language (ML)
ML statements • Stored in a computer’s memory
Computer memory is a sequence of switches. • an “on” switch is represented by 1, • an “off” switch is represented by 0.
ML thus appears to be binary (base-2):
0010111010110101
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Early Computers
... required a programmer to write in ML...
Problem• Easy to make mistakes!• Such mistakes are hard to find!• Not portable -- only runs on one kind of
machine!
Programming was very difficult!
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A Bright Idea
Devise a set of abbreviations (mnemonics) corresponding to the ML statements
Create a program (the assembler) to translate them into ML.
ADD 34, R1MOVE R1,1200CMPR R1, R2
100111001110010110100110110111
Assembler
Assembly languagestatements (mnemonics)
Machine language statements
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Advantages and Disadvantages
More natural than binary.
Much easier to read programs
Much easier to find and fix mistakes
Still not portable to different machines
Each machine had its own set of mnemonics
Each had its own assembler
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High Level Languages
Improvement on assembly language• Devise a set of statements that are close
to human language (if, while, do, ...)• Create a program to translate them into
ML.
The set of statements is called a high level language (HLL) The translation program is called a compiler.
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Contrast Assembler and HLL Compiler
Assembler translates one mnemonic into one ML statement
Compiler translates one HL statement into several ML statements
1010110011110101
0000000000010000
0010111010110101
0000000000010010
0010111011111101
0000000000010100
z = x + y; Compiler
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Advantage of HLLs
Programs are easier to read
Errors are easier to find
Programs are portable from one computer to another• Assumes the language is standard• Just create a new compiler which does the
translation into the correct ML
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Objectives in Programming A program should solve a problem:
Correctly
Efficiently
Readably
In user-friendly fashion
It actually solves the problem
Without wasting time or space
Understandable by another person
In a way that is easy for its user to use
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Summary of "Levels" of Computer Languages
Low levelML in binary language
Medium Level Assembly language
High Levelas in C++
Hard to read, not portable
Mnemonics, easier to read, still not portable
Reads like English and algebra, portable
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Putting It All Together
Programs and applications that are not running are stored on disk.
App
DiskRAMCPUCache
Bus
OS
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Putting It All Together
When you launch a program• OS controls the CPU • Loads the program from disk to RAM.
App
DiskRAMCPUCache
Bus
OS
App
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Putting it all together
The OS then relinquishes the CPU to the program,
Application program begins to run.
App
DiskRAMCPUCache
Bus
OS
AppApp
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The Fetch-Execute CycleOS repeatedly fetches the next instruction (from memory / cache),
Executes it
Stores any results back to memory.
That’s all a computer does: fetch-execute-store, millions of times each second!
App
DiskRAMCPUCache
Bus
OS
AppApp