Transcript CPS120 - Washtenaw Community College

CPS120: Introduction to
Computer Science
Introduction to Computers
Introduction to Computers
 Objectives
– Understand the history of computers
– Understand the components that make up a
desktop PC
– Understand the basics of computer architecture
– Understand the role of an operating system
– Understand the role of assemblers, interpreters,
& compilers
Abstraction
A mental model that removes complex
details
This is a key concept.
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Representing Data
 Data can be numeric, alphabetic, or
alphanumeric
 Computer only uses “on” & “off” within its
circuits
Representing Data: Bits
 Computer only uses “on” & “off” within its
circuits
 Binary number system
– “On”, 1, high state of electricity
– “Off”, 0, low state of electricity
– Bits (0’s and 1’s)
Representing Data: Bytes
 Byte = 8 bits (23)
 256 possible combinations of 8 bits
 Decimal system is cumbersome & awkward
for pc’s
– Can convert from decimal to binary & vice
versa
• ASCII (American standard code for information
interchange)
 128 characters in the 7-bit set
Computing Systems
Hardware: The physical elements of a
computing system (printer, circuit
boards, wires, keyboard…)
Software: The programs that provide the
instructions for a computer to execute
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Layers of a Computing System
Communication
Application
Operating System
Programming
Hardware
Data
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Early History of Computers
 Abacus
 Pascal’s gear-driven counting machine (mid
17th Century)
– His father was a tax collector
 Babbage designed a programmable
computer (1834)
 Joseph Jacquard designed a loom that used
the the punched card to store instructions
(late 18th Century)
Early History of Computing
Ada Augusta, Countess of Lovelace
First Programmer, the loop (mid 19th Century)
Alan Turing (1936)
Turing Machine, Artificial Intelligence Testing
Harvard Mark I, ENIAC, UNIVAC I
Early computers launch new era in mathematics,
physics, engineering and economics
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"Modern" Developments
 Hollerith built machine for US census bureau
& founded IBM (late 19th Century)
 1946, ENIAC used vacuum tubes (Univ of
Penn) - very hot, needed AC, military paid for
this research
 Transistors used in 1950’s, didn’t burn out like
vacuum tubes
 Integrated circuits (chips) used in 1960’s
 Microprocessor used in 1970’s
 Supercomputers, mainframes, minicomputers,
workstations, desktop computers
First Generation Hardware
(1951-1959)
Vacuum Tubes
Large, not very reliable, generated a lot of heat
Magnetic Drum
Memory device that rotated under a read/write
head
Card Readers  Magnetic Tape Drives
Development of these sequential auxiliary storage
devices
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Second Generation Hardware
(1959-1965)
Transistor
Replaced vacuum tube, fast, small, durable,
cheap
Magnetic Cores
Replaced magnetic drums, information available
instantly
Magnetic Disks
Replaced magnetic tape, data can be accessed
directly
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Third Generation Hardware
(1965-1971)
Integrated Circuits
Replaced circuit boards, smaller, cheaper, faster,
more reliable.
Transistors
Now used for memory construction
Terminal
An input/output device with a keyboard and screen
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Fourth Generation Hardware
(1971-?)
Large-scale Integration
Great advances in chip technology
PCs, the Commercial Market,
Workstations
Personal Computers were developed as new
companies like Apple and Atari came into being.
Workstations emerged.
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Parallel Computing
and Networking
•Parallel Computing
•Computers rely on interconnected central
processing units that increase processing speed.
•Networking
•With the Ethernet small computers could be
connected and share resources. A file server
connected PCs in the late 1980s.
•ARPANET and LANs  Internet
•A network of interconnected networks
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First Generation Software
(1951-1959)
Machine Language
Computer programs were written in binary (1s and
0s)
Assembly Languages and translators
Programs were written in artificial programming
languages and were then translated into machine
language
Programmer Changes
Programmers divide into application programmers
and systems programmers
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Representing Instructions:
 Low Level Languages
– Each computer uses its own machine
language
– Assembly is a low-level language close to
machine language
• Assembly languages are different on each
computer
• An assembler converts a program into
machine language
Machine Languages
 different for each computer processor
0100
001101 100000 001101 110001
00101 10001 10000
01110
111001
. . .
Assembly Languages
 different for each computer processor
main
proc pay
mov ax, dseg
mov ax, 0b00h
add ax, dx
mov a1, b1
mul b1, ax
mov b1, 04h
Second Generation Software
(1959-1965)
High Level Languages
Use English-like statements and made
programming easier:
Fortran, COBOL, Lisp (artifical intelligence).
High-Level
Languages
Assembly
Language
Machine
Language
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Third Generation Software
(1965-1971)
Application Package
Systems Software
High-Level Languages
Assembly Language
Machine Language
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Third Generation Software
(1965-1971)
 Systems Software
– utility programs,
– language translators,
– and the operating system, which decides which
programs
– to run and when.
 Separation between Users and Hardware
 Computer programmers now created programs to
be used by people who did not know how to
program
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Fourth Generation Software
(1971-1989)
Structured Programming
BASIC refined, Pascal, C, C++
New Application Software for Users
Spreadsheets, word processors, database
management systems
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Fifth Generation Software
(1990- present)
Microsoft
The Windows operating system, and other Microsoft
application programs dominate the market
Object-Oriented Design
Based on a hierarchy of data objects (i.e. Java)
World Wide Web
Allows easy global communication through the
Internet
New Users
Today’s user needs no computer knowledge
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Computing as a Tool
Programmer / User
Systems Programmer
(builds tools)
Applications Programmer
(uses tools)
Domain-Specific Programs
User with No
Computer Background
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Computing as a Discipline
 Four Necessary Skills
1.
2.
3.
4.
Algorithmic Thinking
Representation
Programming
Design
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System Components
 Hardware
– I/O devices (input/output)
• keyboard, mouse, monitor, etc.
– CPU
– Primary Storage
– Secondary Storage
 Software
Computer Architecture
 Microprocessor (examples Pentium, Pentium II,
PowerPC, etc.)
– includes Bus Interface Unit, Arithmetic & Logic Unit
(ALU), Control Unit, registers
– motherboard is simply the main circuit board that
contains most of these parts
– the CPU (central processing unit) is considered to be
most of these parts taken as a whole
 Bus
– connects the microprocessor to the RAM & ROM
– addresses for data and instructions are important
Storage Devices
 Primary storage
– RAM (Random Access Memory, or just “memory” for
short)
• active data that is being stored, lost if power is cut off so save
often
– ROM (Read-Only Memory)
• commands that are permanently stored on chips
• PC’s use BIOS, Macs use the Toolbox
 Secondary storage
– Hard disk, floppy disks
– Slower method of storage & retrieval but “safer”
Software: Systems Software
 Operating systems
– Controls the hardware components (disks,
CPU, printers, etc.)
– Windows XP, Windows NT/2000, Windows 9X, MS-DOS, OS/2, MacOS, Unix, Linux,
BeOS
Software: Application Software
 Office products
– Word processors
– Spread sheets
– Presentation software
– Email
 Business applications
– General ledger
– Financials
• Accounts payable
• Accounts receivable
– HRMS
– Fixed assets/inventory
Programming Software
 Text Editor
– Used by the programmer while coding the
program in a programming language
• Like a word processor - creates a text file containing
the program's instructions or "source code"
– Examples are “nled” and “vi” editors in Unix systems
– Other editors are NotePad and WordPad which are textbased
Programming Software
 Interpreters
– Translates source code into machine code line by line
 Compiler
– Translates source code into an object file, than uses
linker to create an executable file
• A source module (source code) becomes an "object" module
(compiled module)
• Then it is linked with system modules to become a "load"
module (linked module)
 It is usually more efficient to use a compiler