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  Computing Notes
  => 1 Introduction To Computing
  => 1.1 Computer Hardware
  => 1.2 Computer Software
  => 1.3 The Human-Computer Interface
  => 1.4 Business Information Systems
  => 1.5 Batch Processing
  => 2 Word Processing
  => 2.1 Introduction
  => 2.2 Editing Facilities
  => 2.3 Bullets And Numbering
  => 2.4 Layout Facilities
  => 2.5 Headers And Footers
  => 2.6 Style Controls
  => 2.7 Spelling And Grammar Checking
  => 2.8 Inserting Columns
  => 2.9 Borders And Shading
  => 2.10 Tables
  => 2.11 Inserting Graphics
  => 2.12 Mail Merging
  => 2.13 Macros
  => 3 Programming In QuickBASIC
  => 3.1 Introduction
  => 3.2 Variables, Input And Output
  => 3.3 Arithmetic Operators
  => 3.4 Iteration
  => 3.5 Selection
  => 3.6 Functions
  => 3.7 Subprograms
  => 3.8 Recursion
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  => 3.10 Program Structure
  => 3.11 Jackson Structure Diagrams
  => 3.12 String Processing
  => 4 Data Representation
  => 4.1 Different Computer Codes
  => 4.2 Binary Integers
  => 4.3 Higher Number Bases
  => 4.4 Graphics, Sounds And Other Interpretations
  => 4.5 Fixed Point Binary Numbers
  => 4.6 Floating Point Binary Numbers
  => 4.7 Range And Accuracy
  => 5 Spreadsheets
  => 5.1 Introduction
  => 5.2 General Features
  => 5.3 "What If" Calculations
  => 5.4 Changing The Workbook's Appearance
  => 5.5 Relative And Absolute Reference
  => 5.6 Sorting And Filters
  => 5.7 Charts
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  => 5.9 The IF Function
  => 5.10 Goal Seeker
  => 5.11 Solver
  => 5.12 Macros
  => 6 Files
  => 6.1 File Concepts
  => 6.2 Serial & Sequential Files
  => 6.3 Indexed Sequential Files
  => 6.4 Random Access Files
  => 6.5 Overview of File Processing
  => 7 Standard Algorithms
  => 7.1 Linear Searches
  => 7.2 Binary Search
  => 7.3 Internal Sorting
  => 7.4 External Sorting
  => 8 Legal Issues And Data Security
  => 8.1 The Computer Missuse Act 1990
  => 8.2 The Data Protection Act 1984
  => 8.3 Computer Fraud
  => 8.4 Software Copyright
  => 8.5 Viruses And Trojans
  => 8.6 Security Of Data
  => 8.7 Data Integrity
  => 9 Databases
  => 9.1 Flat-file Databases
  => 9.2 Introduction To Relational Databases
  => 9.3 The Aims Of Database Normalisation
  => 9.4 Security And Integrity Issues
  => 9.5 Database Management
  => 10 Data Structures
  => 10.1 Introduction
  => 10.2 Linear Lists
  => 10.3 Linked Lists
  => 10.4 Queues
  => 10.5 Stacks
  => 10.6 Binary Trees
  => 11 Systems Development
  => 11.1 Introduction
  => 11.2 Analysis
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  => 12 Peripherals
  => 12.1 Input Devices
  => 12.2 Output Devices
  => 12.3 Storage Devices
  => 13 Computer Architecture
  => 13.1 The Processor And Memory
  => 13.2 The Fetch-Execute Cycle
  => 13.3 Data Buses
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  => 14.1 Interpreters
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  => 14.3 Compilation Phases
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  => 15.1 Operating System Functions
  => 15.2 Different OS Modes
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  => 15.4 The Scheduler And Dispatcher
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  => 16 High Level Programming
  => 16.1 High And Low Level Languages
  => 16.2 Language Classification
  => 16.3 Language Generations
  => 16.4 Logic Programming
  => 16.5 Choosing A Programming Language
  => 17 Computers & Communication
  => 17.1 Data Transmission
  => 17.2 Local Area Networks
  => 17.3 Wide Area Networks
  => 17.4 The Internet
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INDIA
17.1 Data Transmission
Section 17.1

Computers & Communication

17.1 Data Transmission

17.1.1 Comms Channels

Coaxial Cable

Coaxial cable (simliar to that used in television systems) has an outer mesh which is 'earthed' and shields the signal in the inner wire. The inner wire carries the signal.

Used in: LAN

Pros

  • Inexpensive
  • Accurate data transfer

Cons

  • Signal degrades over distance
  • Not very easy to lay

Twisted Pair Cable

This uses sets of twisted copper wire pairs.

Used in: LAN

Pros

  • Easy to wire in situe
  • Fast data transfer

Cons

  • Susceptable to interference

Fibre Optic Cable

One of many transparent fibres can relay phases of light.

Used in: MAN and WAN (internet backbone)

Pros

  • Very fast data transfer rate
  • No electromagnetic interference
  • Physically secure
  • Less signal degradation over distance

Cons

  • Cost
  • Cable cannot bend around tight corners
  • Difficult to interface with computer

Microwave Transmission

Data is encoded on a microwave signal.

Used in: MAN

Pros

  • No cost of wiring and associated disruption
  • Reasonable bandwidth

Cons

  • Limited to line of sight

Satellite Transmission

A one or two-way link can be established by using a satellite (in geosynchronus orbit) and a dish.

Used in: WAN

Pros

  • Good bandwidth
  • No wiring or boosters needed

Cons

  • Expensive
  • Possibly insecure

17.1.2 Transmission Directions

Simplex

Data can only be transmitted in one direction.

Half-Duplex

Data can be sent in both directions but not at the same time.

OR

Full-Duplex

Data can be sent in both directions at the same time.

17.1.3 Transmission Rate

The speed at which data is transmitted is measured in bits per second (bps).

The bandwidth is the maximum speed at which data can be sent along a communication channel.

17.1.4 Error Detection

A parity bit can be transmitted with the code for each character.

An element of redundancy can be introduced with 2D parity. This allows corrupted data to be recovered.

17.1.5 Modulation And Digital Transmission

Analogue Systems

MODEM stands for Modulator-Demodulator.

To send digital data, the data is imposed or modulated onto an analogue wave.

The reverse process (demodulation) retrieves the digital information.

Digital Systems

Data is sent digitally via:

  • An ISDN line
  • A LAN connection
  • A digital radio network
  • A phone line with ADSL

ISDN (Integrated Services Digital Network)

Data is sent digitally down a special ISDN line.

ADSL (Asymetric Digital Subscriber Line)

This has a maximum bandwidth of 9Mbps and runs over a standard telephone line.

17.1.6 Parallel To Serial Transmission

Parallel transmission is not pratical for long distance communication. This is because of the cost of manufacturing the wires.

17.1.7 Multiplexing

Multiplexing allows more than one signal to be sent over a single link at one time.

There are two main methods of doing this:

Time Division Multiplexing

The transmission time is broken up into slices and each device wishing to transmit can take a packet in turn.

Frequency Division Multiplexing

Different frequency carrier waves are used to send many signals over the link. A high bandwidth is required for this.

17.1.8 Data Compression

Data compression is frequently used when transmitting large amounts of data.

At the heart of the process is the method of looking for repeated patterns and replacing them by one copy of the bit pattern plus the number of times it occurs.


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