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CSCE 1030
Computer Science 1
Computer Organization and Networking
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Components of a Computer System
Hardware Software
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Hardware Components – Von Neumann Architecture
CPU
Unit
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Secondary Storage
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Central Processing Unit (CPU)
A microprocessor which is an integrated circuit (IC) that performs all calculations, operations in computer
2 components Arithmetic Logic Unit Control Unit
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CPU – cont’d
ALU Arithmetic operations (+, -, *, /) Bitwise logic operations (AND, NOT, OR,
XOR) Shift operations
CU Controls the flow of data through CPU Coordinates the activities of other units
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Control Unit (CU)
Performs the Fetch/Execute cycle:
Instruction Fetch (IF)
Instruction Decode (ID)
Data Fecth (DF)
Instruction Execution (EX)
Result Return (RR)
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Fetch/Execute Cycle
Computer before executing an ADD instruction
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Fetch/Execute Cycle – cont’d
Instruction Fetch
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Fetch/Execute Cycle – cont’d
Instruction Decode
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Fetch/Execute Cycle – cont’d
Data Fetch
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Fetch/Execute Cycle – cont’d
Execute
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Fetch/Execute Cycle – cont’d
Result Return
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Machine Language Instructions
Can be decoded and executed by control unit
Parts of instructions
Operation code (op code)
Unique unsigned-integer code assigned to each machine language operation
Address fields
Memory addresses of the values on which operation will work
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Figure 5.14
Typical Machine Language Instruction Format
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Machine Language Instructions (continued)
Operations of machine language
Data transfer operations
Move values to and from memory and registers
Arithmetic/logic operations
Perform ALU operations that produce numeric values
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Machine Language Instructions (continued)
Operations of machine language (continued)
Compare operations
Compare two values and set an indicator on the basis of the results of the compare; set register bits
Branch operations
Jump to a new memory address to continue processing
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Control Unit Registers and Circuits
Parts of control unit
Links to other subsystems
Instruction decoder circuit
Two special registers Program counter (PC)
Stores the memory address of the next instruction to be executed
Instruction register (IR) Stores the code for the current instruction
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Figure 5.16
Organization of the Control Unit Registers and Circuits
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Storage
Primary Storage (Memory) ROM RAM
Secondary (Auxiliary) Storage Hard disk (HDD) Tape CD and DVDs Flash disk, etc..
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Memory – cont’d
Read Only Memory (ROM) Non-volatile: content is always there Only manufacturer can write on ROM, once
written the content cannot be changed Stores the initial program that runs when the
computer is powered (bootstrapping) Many complex functions, such as translators
for high-level languages, and OSes are stored in ROM
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Memory
Random Access Memory (RAM) Volatile – content is lost when computer is off Provides faster access than secondary storage Can be read and written Is like the working memory Memory made of addressable cells (8 bits) All memory cells accessed in equal time Memory address
Unsigned binary number N long Address space is then 2N cells
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Figure 5.3
Structure of Random Access Memory
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RAM
Parts of the memory subsystem
Fetch/store controller
Fetch: Retrieve a value from memory
Store: Store a value into memory
Memory address register (MAR)
Memory data register (MDR)
Memory cells with decoder(s) to select individual cells
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Memory and Cache (continued)
Fetch operation
The address of the desired memory cell is moved into the MAR
Fetch/store controller signals a fetch, accessing the memory cell
The value at the MAR’s location flows into the MDR
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Memory and Cache (continued)
Store operation
The address of the cell where the value should go is placed in the MAR
The new value is placed in the MDR
Fetch/store controller signals a store, copying the MDR’s value into the desired cell
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Memory and Cache (continued)
Memory register
Very fast memory location
Given a name, not an address
Serves some special purpose
Modern computers have dozens or hundreds of registers
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Figure 5.7Overall RAM Organization
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Cache Memory
Memory access is much slower than processing time
Faster memory is too expensive to use for all memory cells
Locality principle
Once a value is used, it is likely to be used again
Small size, fast memory just for values currently in use speeds computing time
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Secondary Storage
Memory external to the main body of the computer Stores large amounts of data and programs for future
use For execution, the data and programs are read into
primary storage. Non-volatile: Content does remains when the power
is turned off. Cheap and larger in capacity as compared to RAM Also called mass storage
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Secondary Storage – cont’d
Mass storage devices Direct access storage device
Hard drive, CD-ROM, DVD Uses its own addressing scheme to access
data
Sequential access storage device Tape drive Stores data sequentially Used for backup storage these days
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Secondary Storage – cont’d
Direct access storage devices Data stored on a spinning disk Disk divided into concentric rings (sectors) Read/write head moves from one ring to
another while disk spins Access time depends on
Time to move head to correct sector Time for sector to spin to data location
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Figure 5.8
Overall Organization of a Typical Disk
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Peripheral Devices (Input – Output Units) Connected to computer main body physically Used to input and/or output data I/O controller
Intermediary between central processor and I/O devices
Processor sends request and data, then goes on with its work
I/O controller interrupts processor when request is complete
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Figure 5.9
Organization of an I/O Controller
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Software
Programs that are stored in computer 2 types
Systems Programs OSes, such as Windows, Mac, Linux, Unix, etc.
Application Programs Specific programs, such as payroll program,
accounting program, etc.
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Computer Networks
A computer network is a group of interconnected computers to share resources and exchange data through a communications link
Requires two or more individual systems something to share, e.g. printer, file A transmission medium A protocol, i.e. rules of communication
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Why do we need networks?
Distribute computation task among different computers – parallel processing
Access to remote resources Personal communications (e-mail, live chat,
audio/video conferencing) Internet!! etc.
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Communication Links
Switched, dial-up telephone line
A circuit is temporarily established between the caller and callee
Analog medium
Requires modem at both ends to transmit information produced by a computer
Computer produces digital information
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Figure 7.1 Two Forms of Information Representation
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Figure 7.2
Modulation of a Carrier to Encode Binary Information
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Communication Links (continued)
Dial-up phone links
Transmission rate: 56,000 bps (56 Kbps)
Broadband
Transmission rate: exceeding 128,000 bps (128 Kbps)
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Communication Links (continued)
Options for broadband communications
Home use
Digital subscriber line (DSL)
Cable modem
Commercial and office environment
Ethernet
Fast Ethernet
Gigabit Ethernet
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Figure 7.3
Transmission Time of an Image at Different Transmission Speeds
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Communication Links (continued)
Wireless data communication
Uses radio, microwave, and infrared signals
Enables “mobile computing”
Types of wireless data communication
Wireless local access network
Wireless wide-area access network
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Local Area Networks
Local area network (LAN)
Connects hardware devices that are in close proximity
The owner of the devices is also the owner of the means of communications
Common wired LAN topologies Bus
Ring
Star
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Figure 7.4
Some Common LAN Topologies
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Figure 7.5: An Ethernet LAN ImplementedUsing Shared Cables
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Figure 7.6
An Ethernet LAN Implemented Using a Hub
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Wide Area Networks
Wide area networks (WANs)
Connect devices that are across town, across the country, or across the ocean
Users must purchase telecommunications services from an external provider
Dedicated point-to-point lines
Most use a store-and-forward, packet-switched technology to deliver messages
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Figure 7.7
Typical Structure of a Wide Area Network
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Overall Structure of the Internet
All real-world networks, including the Internet, are a mix of LANs and WANs
Example: a company or a college
One or more LANs connecting its local computers
Individual LANs interconnected into a wide-area “company network”
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Figure 7.8(a)
Structure of a Typical Company Network
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Overall Structure of the Internet (continued)
Internet Service Provider (ISP)
A wide-area network
Provides a pathway from a specific network to other networks, or from an individual to other networks
ISPs are hierarchical
Interconnect to each other in multiple layers to provide greater geographical coverage
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Figure 7.8(b)
Structure of a Network Using an ISP
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Figure 7.8(c)Hierarchy of Internet Service Providers
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Overall Structure of the Internet (continued)
Internet
A huge interconnected “network of networks”
Includes nodes, LANs, WANs, bridges, routers, and multiple levels of ISPs
Early 2003 170 million nodes (hosts)
Hundreds of thousands of separate networks located in over 225 countries
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Communication Protocols
A protocol
A mutually agreed upon set of rules, conventions, and agreements for the efficient and orderly exchange of information
TCP/IP
The Internet protocol hierarchy
Governs the operation of the Internet
Five layers
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Figure 7.10
The Five-Layer TCP/IP Internet Protocol Hierarchy
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Physical Layer
Protocols govern the exchange of binary digits across a physical communication channel
Goal: create a “bit pipe” between two computers
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Data Link Layer
Protocols carry out
Error handling
Framing
Creates an error-free “message pipe”
Composed of two services
Layer 2a: medium access control
Layer 2b: logical link control
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Data Link Layer (continued)
Medium access control protocols
Determine how to arbitrate ownership of a shared line when multiple nodes want to send at the same time
Logical link control protocols
Ensure that a message traveling across a channel from source to destination arrives correctly
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Network Layer
Delivers a message from the site where it was created to its ultimate destination
Critical responsibilities
Creating a universal addressing scheme for all network nodes
Delivering messages between any two nodes in the network
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Network Layer (continued)
Provides a true “network delivery service”
Messages are delivered between any two nodes in the network, regardless of where they are located
IP (Internet Protocol) layer
Network layer in the Internet
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Transport Layer
Provides a high-quality, error-free, order preserving end-to-end delivery service
TCP (Transport Control Protocol)
Primary transport protocol on the Internet
Requires the source and destination programs to initially establish a connection
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Figure 7.15
Logical View of a TCP Connection
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Application Layer
Implements the end-user services provided by a network
There are many application protocols, including:
HTTP
SMTP
POP3
IMAP
FTP
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Figure 7.16
Some Popular Application Protocols on the Internet
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Application Layer (continued)
Uniform Resource Locator (URL)
A symbolic string that identifies a Web page
Form
protocol://host address/page
The most common Web page format is hypertext information
Accessed using the HTTP protocol
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Network Services and Benefits
Services offered by computer networks
Electronic mail (email)
Bulletin boards
News groups
Chat rooms
Resource sharing Physical resources
Logical resources
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Network Services and Benefits (continued)
Services offered by computer networks
Client-server computing
Information sharing
Information utility
Electronic commerce (e-commerce)
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A Brief History of the Internet and the World Wide Web: The Internet
August 1962: first proposal for building a computer network
Made by J. C. R. Licklider of MIT
ARPANET
Built by the Advanced Research Projects Agency (ARPA) in the 1960s
Grew quickly during the early 1970s
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The Internet (continued)
NSFNet: A national network built by the National Science Foundation (NSF)
October 24, 1995: Formal acceptance of the term “Internet”
Internet service providers start offering Internet access once provided by the ARPANET and NSFNet
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Figure 7.20State of Networking in the Late 1980s
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The World Wide Web Development completed in May 1991
Designed and built by Tim Berners-Lee
Components
Hypertext A collection of documents interconnected by
pointers called links
URL (Uniform Resource Locator) The worldwide identification of a Web page
located on a specific host computer
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Figure 7.21
Hypertext Documents
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