Introduction to Library & Information Sciences

Course Code: 5501

Computer Hardware, Software, LAN&WAN

Historical Background: LANsIn 1970s a new trend began in computing

i.e., shifting from large centralized mainframes occupying a room, towards physically smaller, yet higher performance minicomputers. The first microprocessor system was introduced around 1971.

Microprocessor: An integrated circuit that contains all the functions of a central processing unit of a computer.

Local Area Network (LAN)LAN opened up the possibility of attaining

advantages of workstations, without losing the centralized mainframe systems. Information could flow between individual workstations at speeds which, to a large extent, hid the fact that users were not working on a single system.

Chain Point to Point Star

Component of LANCommunication Medium

Copper wire, optical fiber, radio link etc. Bandwidth

capacity of a medium to carry data (measured in mega bits per second)Multi-addressing or Broadcasting

addresses could be of other users such as printer, scanner etc

Component of LANDistributed Control

control not limited to one use/computer but distributed among members of the network as democracyFacilities

user can enter a job from any computer connected to LAN i.e., exchange files Range

communication medium limits it to premises within a building or within an area

Transmission Media & TechniquesTerminal to Host TrafficApplications for graphic images is Megabits

per second

The medium chosen will have to accommodate current as well as future requirements over the system’s expected life time of 15 years or more.

Transmission Media & TechniquesBaseband TransmissionModulated TransmissionBroadband Transmission

Wide Area Network (WANs)WANs maybe an extension of a LAN, but

involve distances in the range of thousands of miles, requiring media different from LANs and also different hardward/software.

Historical Background: WANsIn 1960s ARPA (now Defense Advanced

Research Projects Agency of US Department of Defense – DARPA), began research on subject of computer networks by providing grants to computer science department at many US Universities and few private corporations. This research led to an experimental four node network that went on air in Dec 1969 known as ARPANET.

WAN ConceptsBasics

Circuit Switching (Mode of transmitting information between two points)

Dial up Line (circuit switched line operable by dialing a number)

Leased Line (Radio channel or a satellite link etc)

WAN ConceptsBasics

Packet Switching:http://www.google.com.pk/imgres?q=packet+switching&um=1&hl=en&biw=1280&bih=816&tbm=isch&tbnid=kCRNwPO2HxcwRM:&imgrefurl=http://www.boerner.net/jboerner/%3Fp%3D7540&docid=uxZ2NrsPsNfH-M&imgurl=http://www.boerner.net/jboerner/wp-content/uploads/2010/01/packet.switching.gif&w=545&h=239&ei=j9YeUqT9JKmU0AW-j4GAAw&zoom=1&ved=1t:3588,r:2,s:0,i:90&iact=rc&page=1&tbnh=148&tbnw=339&start=0&ndsp=13&tx=141&ty=77

WAN ConceptsBasics

X.25: It is CCITT (Comite Consultatif International Telegraphique et Telephonique) standard describing how communication devices package data into packets and how these packets are routed.

Another X.75 defines how two packet switched networks communicate.

PDNs (Public Data Networks): Different communications protocols to talk to each other and transfer bulk data. SVC (Switched Virtual Circuit) (Temporary logical

path) PVC (Permanent Virtual Circuit) (Permanent)

ModemAn electronic device that convert computer’s

digital signals into electrical audio signals, such that they can be transmitted over telephone lines.

Telephone lines were designed and installed for analog speech communication, however, computer speak digital, therefore, a modem is required.

TerminologyHost (Computer providing network services)Node (Unique identification)Account (name, password)E. mail (Electronic Mail)Mailbox (Special Account)FTP (File Transfer Protocol – Exchange Files

b/w 2 computers)TELNET (a user on one computer to log on to

another computer that is part of the same network)

Remote Login (Login a remote computer)News Group (Electronic forum of discussion)Mailing List (facility to receive messages by

email)

Logical Structure of a PC

Input Unit

Keyboard Mouse

Graphic Tablet

Light Pen

Input Unit

Joystick Graphic Scanners

Microphone

Mass Storage DevicesDisk Drives

Floppy Diskette Drive

Hard Disk

Floptical Disk Drive

Mass Storage DevicesCassette Tape & Tape Backup Unit

CD-ROM

Central Processing Unit (CPU)

Memory or Primary Storage UnitRead only Memory (ROM) (Permanent

Storage)ROM PROM (Programmable ROM)EPROM (Erasable Programmable ROM))EEPROM (Electrically Erasable Programmable

ROM)

Random Access Memory (RAM) (Temporary Storage)SRAM (Static RAM)DRAM (Dynamic RAM)SIMM (Single In-Line Memory Module)SIP (Single In-Line Package)

Memory or Primary Storage UnitRandom Access Memory (RAM) (Temporary

Storage)System RAMShadow RAMCache RAMVideo RAM (VRAM)

Output Unit

Computer Program (Software)DISK Operating System (DOS)

Utilities (assists in operation of computer but does not perform main work i.e., detect or clean virus)

Applications Software (applications software or applications program is the one that performs useful work, not related to computer itself i.e., MS Office, Corel Draw etc.)

Information Storage

Information Storage & RetrievalFunctions in Storage and Retrieval

Data Acquisition (Must be selective)Vocabulary of Terms (must words from

respective document )Description Record Format File Indexes Linkage among recordsRequestsRecord SearchRetrieval and Representation

Type of SystemDatabase System

A database is an organized collection of dataReference Retrieval System

Reference-retrieval systems store references to documents rather than the documents themselves

DocumentCombine a reference database system with the

ability to retrieve desired document pages, text or image and print or display them

TextFull Text Retrieval

ImageStore and retrieve image

Storing the DataTopic treats the physical organization of data

in terms of speed of access, storage requirements, and flexibility of access.

Three major types of file organization Sequential

can produce easily, but they have a slower access time

Random access fast access time, but cannot easily produce

sequential listsIndexed sequential

too long to find the item

Storing the DataThree major types of file organization

Sequential Data is searched by key

Random access Key is used to compute the address of a storage

location.Indexed sequential

Index is made up of the key and address at which the data bearing that key is stored

Qualities in Selection File StructureActivity

How many of the records in a file are accessed whenever the file is processed

VolatilityNumber of records deleted and added to a file.

The records added called insertions, and deleted called deletions

Frequency of AccessHow often we query (access) the file

Volume or SizeNumber of records or number of characters

Response Time Required