network topology &transmission media

Chapter 9  Networks and Communications


Network topology

A network topology refers to the layout of the computers and devices in a communications network


Transmission media


on which data, instructions, or information travel in a communications system.The amount of data, instructions, and information that can travel over a communications channel sometimes is called the bandwidth.

Network topology
Bus Topology

Advantages
It is easy to handle and implement. 
It is best suited for small networks.


Disadvantages
The cable length is limited. This limits the number of stations that can be connected.
This network topology can perform well only for a limited number of nodes.


Ring Topology

Advantage
The data being transmitted between two nodes passes through all the intermediate nodes. A central server is not required for the management of this topology.

Disadvantages
The failure of a single node of the network can cause the entire network to fail.
The movement or changes made to network nodes affects the performance of the entire network.


Star Topology

Advantages
Due to its centralized nature, the topology offers simplicity of operation. 
It also achieves an isolation of each device in the network.

Disadvantage
The network operation depends on the functioning of the central hub. Hence, the failure of the central hub leads to the failure of the entire network.

Transmission media
advantages

• used for long distance communication
• high speed data transmission
• many reciver stations can receive signal from the same sender station

disadvantages

• very costly

Mashup

Chapter 9 Networks and Communication 


Mashup(web application hybrid)

In Web development, a mashup is a Web page or application that uses and combines data, presentation or functionality from two or more sources to create new services. The term implies easy, fast integration, frequently using open APIs and data sources to produce enriched results that were not necessarily the original reason for producing the raw source data.

The main characteristics of the mashup are combination, visualization, and aggregation. It is important to make existing data more useful, moreover for personal and professional use. To be able to permanently access the data of other services, mashups are generally client applications or hosted online.

In the past years, more and more Web applications have published APIs that enable software developers to easily integrate data and functions instead of building them by themselves. Mashups can be considered to have an active role in the evolution of social software and Web 2.0. Mashup composition tools are usually simple enough to be used by end-users. They generally do not require programming skills and rather support visual wiring of GUI widgets, services and components together. Therefore, these tools contribute to a new vision of the Web, where users are able to contribute.

National Science Foundation Network (NSF net)

Chapter 2 Fundamentals of the World Wide Wed and Internet

National Science Foundation Network (NSF net)

The National Science Foundation Network (NSFNET) was a program of coordinated, evolving projects sponsored by the National Science Foundation (NSF) beginning in 1985 to promote advanced research and education networking in the United States. NSFNET was also the name given to several nationwide backbone networks that were constructed to support NSF's networking initiatives from 1985-1995. Initially created to link researchers to the nation's NSF-funded supercomputing centers, through further public funding and private industry partnerships it developed into a major part of the Internet backbone.

History

Following the deployment of the Computer Science Network (CSNET), a network that provided Internet services to academic computer science departments, in 1981, the U.S. National Science Foundation (NSF) aimed to create an academic research network facilitating access by researchers to the supercomputing centers funded by NSF in the United States.

In 1985, NSF began funding the creation of five new supercomputing centers: the John von Neumann Computing Center at Princeton University, the San Diego Supercomputer Center (SDSC) on the campus of the University of California, San Diego (UCSD), the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign, the Cornell Theory Center at Cornell University, and the Pittsburgh Supercomputing Center (PSC), a joint effort of Carnegie Mellon University, the University of Pittsburgh, and Westinghouse.

Hibernate VS Sleep ( computer )

chapter 8  operating  system 

Hibernation (computing)

Hibernation in computing is powering down a computer while retaining its state.
Upon hibernation, the computer saves the contents of its random access memory (RAM) to a hard disk or other non-volatile storage. Upon resumption, the computer is exactly as it was upon entering hibernation.
When used to save power, hibernation is similar to sleep mode and saves more power at the cost of slower resumption.

Uses of hibernation 

Hibernation saves electrical power. After hibernating, the hardware is completely powered down (just like for a regular shutdown). Therefore a hibernated machine uses no more electrical power than one which is switched off. Meanwhile, hibernation is a means of avoiding the burden of saving unsaved data before shutting down and restoring all running programs after powering back on.

Hibernation is used in laptops, which have limited battery power available. It can be set to happen automatically on a low battery alarm. Most desktops also support hibernation, mainly as a general energy saving measure.

sleep mode

Many systems also support a low-power sleep mode or stand by mode in which the processing functions of the machine are powered down, using a little power to preserve the contents of RAM and support waking up; wakeup is almost instantaneous.
The advantage of sleep mode is that resuming is much quicker than for hibernation. A hibernated system must start up, then read back data to RAM on resuming, which typically takes about ten seconds or more. A system in sleep mode only needs to power up the CPU and display, which is almost instantaneous. On the other hand, a system in sleep mode still consumes some power, while a hibernated system does not require any power at all. A sleeping computer is a case of a device consuming standby power, covered by regulations in many countries limiting such power under the One Watt Initiative to one watt from 2010. Since these facilities were introduced, most systems have come to offer both sleep mode and hibernation.

Hybrid sleep

Sleep mode and hibernation can be combined: The contents of RAM are copied to non-volatile storage and the computer enters sleep mode. This approach combines the benefits of sleep mode and hibernation: The machine can resume instantaneously, and its state, including open and unsaved files, will survive a power outage.

Difference Between Active-matrix display and passive-matrix display

 CIS1006: INTRODUCTION TO INFORMATION SYSTEMS 
 Chapter 6    Understanding Output

Liquid crystal display (LCD) uses a liquid  compound to present information on a display  device

LCD monitors and LCD screens typically produce color using either active-matrix or passive-matrix technology.

Active-matrix display :

An active-matrix display, also known as a TFT (thin-film transistor) display, uses a separate transistor to apply charges to each liquid crystal cell and thus displays high-quality color that is viewable from all angles.

Passive-matrix display :

A passive-matrix display uses fewer transistors, requires less power, and is less expensive than an active-matrix display. The color on a passive-matrix display often is not as bright as an active-matrix display. Users view images on a passive-matrix display best when working directly in front of it.

Mouse operations

Triple-click

Mouse Action: Quickly press and release the left mouse button three times without moving the mouse .Example ,select a paragraph.

Right‐drag

Mouse Action : Point to an item , hold down the right mouse button , move  the  item to the  desired location on screen , and then release the right mouse  button. Example, display a shortcut menu after moving an object from one location  to another.

Free‐spin wheel 

Mouse Action :Whirl the wheel forward or backward so the it spins freely on its owns . Example ,scroll through hundreds of pages in seconds .

Press wheel

Mouse Action : Press the wheel button while moving the mouse. Example , Scroll continuously.

Tilt wheel

Mouse Action: Press the wheel toward the right or left. Example , Scroll horizontally (left and right).

World Book Day ( 23rd April 2012 )

World Book and Copyright Day (also known as International Day of the Book or World Book Days)

 is a yearly event on 23 April, organized by UNESCO to promote reading, publishing and copyright. The Day was first celebrated in 1995 and in 2012 the UK World Book day was celebrated on 1 March 2012.

World Book Day was celebrated for the first time on 23 April. The connection between 23 April and books was first made in 1923 by booksellers in Spain as a way to honor the author Miguel de Cervantes who died on that day.

        In 1995, UNESCO decided that the World Book and Copyright Day would be celebrated on this date because of the Catalonia festival and because the date is also the anniversary of the birth and death of William Shakespeare, the death of Miguel de Cervantes, Inca Garcilaso de la Vega and Josep Pla, and the birth of Maurice Druon, Manuel Mejía Vallejo and Halldór Laxness.

        Although 23 April is often stated as the anniversary of the deaths of both William Shakespeare and Miguel de Cervantes, this is not strictly correct. Cervantes died on 22 April and was buried on 23 April according the Gregorian calendar; however, at this time England still used the Julian calendar. Whilst Shakespeare died on 23 April by the Julian calendar in use in his own country at the time, he actually died eleven days after Cervantes because of the discrepancy between the two date systems. The apparent correspondence of the two dates was a fortunate coincidence for UNESCO. 

    In the  Spanish  region  of  Catalonia , on 23rd April , a rose  is  exchanged  for each  book  received 

Activity for IT students ( 12-04-2012 Thursday )

On last Thursday, all our IT students have a meeting at 2pm-4pm. Our agenda of meeting is about extra curriculur. Around 2pm-2:30pm we gather at Theater 2 at Level 4 with Mr.John & Mr.Gilbert. After and later we went to the ballet dancing room. Once we enter the ballet room we feel very warm and smelly.... Start of the program Ms.Carol have a warming up session with us. Later on Ms.Carol play funny games with us.. Such as playing jump to outer space, boat sinking and many more... 

Difference Between Multi‐core processor ，Dual‐core processor and Quad‐core processor

Multi‐core processor

A multi-core processor is a single computing component with two or more
independent actual processors (called "cores"), which are the units that read
and execute program instructions. The instructions are ordinary CPU
instructions such as add, move data, and branch, but the multiple cores can
run multiple instructions at the same time, increasing overall speed for
programs amenable to parallel computing. Manufacturers typically integrate
the cores onto a single integrated circuit die (known as a chip multiprocessor
or CMP), or onto multiple dies in a single chip package.

A many-core  processor is a multi-core processor in which the number of cores is large
enough that traditional multi-processor techniques are no longer
efficient[citation needed] — largely because of issues with congestion in
supplying instructions and data to the many processors. The many-core
threshold is roughly in the range of several tens of cores; above this threshold
network on chip technology is advantageous.

 Dual-core and Quad-core

A dual-core processor has two cores (e.g. AMD Phenom II X2, Intel Core Duo),
a quad-core processor contains four cores (e.g. AMD Phenom II X4, Intel's quadcore
processors, see i3, i5, and i7 at Intel Core)