Data About Networking

1.1 Growth Of Computer Networking
Computer networking has grown explosively. Since the 1970s, computer communication
has changed from an esoteric research topic to an essential part of the infrastructure.
Networking is used in every aspect of business, including advertising, production,
shipping, planning, billing, and accounting. Consequently, most corporations have multiple
networks. Schools, at all grade levels from elementary through post-graduate, are
using computer networks to provide students and teachers with instantaneous access to
online information. Federal, state, and local government offices use networks, as do
military organizations. In short, computer networks are everywhere.
The growth and uses of the global Internet† are among the most interesting and exciting
phenomena in networking. In 1980, the Internet was a research project that involved
a few dozen sites. Today, the Internet has grown into a production communication
system that reaches all populated countries of the world. Many users have highspeed
Internet access through cable modems, DSL, or wireless technologies.
The advent and utility of networking has created dramatic economic shifts. Data
networking has made telecommuting available to individuals and has changed business
communication. In addition, an entire industry emerged that develops networking technologies,
products, and services. The importance of computer networking has produced
a demand in all industries for people with more networking expertise. Companies need
workers to plan, acquire, install, operate, and manage the hardware and software systems
that constitute computer networks and internets.
1.2 Introduction And Overview Chap
quired because all programmers are expected to design and implement application
software that can communicate with applications on other computers.
1.2 Why Networking Seems Complex
Because computer networking is an active, exciting field, the subject seems complex.
Many technologies exist, and each technology has features that distinguish it from
the others. Companies continue to create commercial networking products and services,
often by using technologies in new unconventional ways. Finally, networking seems
complex because technologies can be combined and interconnected in many ways.
Computer networking can be especially confusing to a beginner because no single
underlying theory exists that explains the relationship among all parts. Multiple organizations
have created networking standards, but some standards are incompatible with
others. Various organizations and research groups have attempted to define conceptual
models that capture the essence and explain the nuances among network hardware and
software systems, but because the set of technologies is diverse and changes rapidly,
models are either so simplistic that they do not distinguish among details or so complex
that they do not help simplify the subject.
The lack of consistency in the field has produced another challenge for beginners:
instead of a uniform terminology for networking concepts, multiple groups each attempt
to create their own terminology. Researchers cling to scientifically precise terminology.
Corporate marketing groups often associate a product with a generic technical term or
invent new terms merely to distinguish their products or services from those of competitors.
Thus, technical terms are easily confused with the names of popular products. To
add further confusion, professionals sometimes use a technical term from one technology
when referring to an analogous feature of another technology. Consequently, in addition
to a large set of terms and acronyms that contains many synonyms, networking
jargon contains terms that are often abbreviated, misused, or associated with products.

power generation cogeneration

In a bid to help reduce the environmental burden of waste disposal, municipalities across the nation are beginning to harness the energy that escapes into the atmosphere as heat during trash incineration. Inefficiency has long plagued this type of power generation, but new technologies are making the option attractive to the many plants that are now adopting them.
Plenty of Power from Garbage
Not surprisingly, waste incineration, like other forms of energy generation, involves using heat obtained by burning fuel to boil water; steam-driven turbines then generate electricity. What is surprising is the long history behind waste incineration. An Osaka incinerator was outfitted to produce electricity in 1965, and the late 1970s saw a similar operation by a Tokyo factory looking to sell power to electric utility companies. The practice has been growing steadily since then. Of the some 2,000 incinerators in the nation, 130 were producing a total of 640 megawatts of power, or an oil equivalent of 232,000 kiloliters, as of the end of March 1996. This is far more than the amount currently produced by solar power (400 kl) or wind power (1,000 kl).
Waste-incineration is a stable source of energy, being unaffected by changes in the weather as are solar and wind power. Moreover, other thermal, hydroelectric, and nuclear plants are generally built in remote places; as a result, the cost of getting the energy to the consumer is higher. Waste incinerators, however, have access to more fuel in highly populated areas, and large generators are easy to install. And the need to burn the trash at a constant temperature to produce a steady flow of power affords the additional benefit of reducing the amounts of dioxin and other dangerous substances produced.
There is a downside to this method of generating power, though. In general, the efficiency of thermal electricity production goes up along with the temperature of the steam. But garbage burned at high temperatures gives off chlorine and other corrosive gases that can damage the steam pipes. Steam produced by waste incineration is therefore kept between 250 and 300 degrees centigrade, giving the method an efficiency of only 15% to 16%, compared with close to 40% efficiency for other types of thermal power generation where the steam is heated to between 500 and 600 degrees. But recent technological developments are now making it possible to cope with this problem.
Toward More Efficient Generation
Two methods for boosting the efficiency of waste-incineration power have been developed. The first involves using more heat-resistant materials for the steam pipes in the plants. One incinerator in Saitama Prefecture that has been generating electricity since 1995 has been able to hike its efficiency to 21% by replacing its pipes with chlorine-resistant stainless steel conduits and boosting steam temperature to 380 degrees. The plant is now able to generate 720 kilowatts per ton of trash, as opposed to the 200 to 300 kilowatts that a normal incinerator is able to obtain.
The second technological development is a dual generating system involving both gas turbines and trash incineration. Turbines are powered by natural gas to produce electricity; the exhaust from the turbines, which reaches temperatures from 500 to 600 degrees, is then used to further heat the steam produced by the trash incinerator to about 400 degrees. This type of power plant, called a "super waste incinerator," has been generating electricity on a trial basis since the end of last year in both Gunma Prefecture and in the city of Sakai, Osaka Prefecture. Another "super" plant should go on line in Kitakyushu, Fukuoka Prefecture, in summer 1998. The Gunma dual-system plant is capable of producing 25 megawatts of electricity and has achieved an efficiency rate of over 30%.
These highly efficient waste-incineration power plants consume about 20% to 30% of their generated electricity themselves; the remainder is sold back to utility companies. One plant in Saitama Prefecture uses one-third of the 24 megawatts it generates and earns 1.3 billion yen (11.3 million dollars at 115 yen to the dollar) annually by selling the remaining two-thirds of the electricity. This is quite a difference from before the switch to high-efficiency equipment, when the plant paid 180 million yen (1.6 million dollars) each year for the power it needed.
Next on the drawing board are ways to reduce the cost of plant construction and make it easier to store electricity produced overnight until it can be used. As these new technologies are developed, the number of waste incinerators producing electricity is sure to leap.

from junk to juice

In a bid to help reduce the environmental burden of waste disposal, municipalities across the nation are beginning to harness the energy that escapes into the atmosphere as heat during trash incineration. Inefficiency has long plagued this type of power generation, but new technologies are making the option attractive to the many plants that are now adopting them.
Plenty of Power from Garbage
Not surprisingly, waste incineration, like other forms of energy generation, involves using heat obtained by burning fuel to boil water; steam-driven turbines then generate electricity. What is surprising is the long history behind waste incineration. An Osaka incinerator was outfitted to produce electricity in 1965, and the late 1970s saw a similar operation by a Tokyo factory looking to sell power to electric utility companies. The practice has been growing steadily since then. Of the some 2,000 incinerators in the nation, 130 were producing a total of 640 megawatts of power, or an oil equivalent of 232,000 kiloliters, as of the end of March 1996. This is far more than the amount currently produced by solar power (400 kl) or wind power (1,000 kl).
Waste-incineration is a stable source of energy, being unaffected by changes in the weather as are solar and wind power. Moreover, other thermal, hydroelectric, and nuclear plants are generally built in remote places; as a result, the cost of getting the energy to the consumer is higher. Waste incinerators, however, have access to more fuel in highly populated areas, and large generators are easy to install. And the need to burn the trash at a constant temperature to produce a steady flow of power affords the additional benefit of reducing the amounts of dioxin and other dangerous substances produced.
There is a downside to this method of generating power, though. In general, the efficiency of thermal electricity production goes up along with the temperature of the steam. But garbage burned at high temperatures gives off chlorine and other corrosive gases that can damage the steam pipes. Steam produced by waste incineration is therefore kept between 250 and 300 degrees centigrade, giving the method an efficiency of only 15% to 16%, compared with close to 40% efficiency for other types of thermal power generation where the steam is heated to between 500 and 600 degrees. But recent technological developments are now making it possible to cope with this problem.
Toward More Efficient Generation
Two methods for boosting the efficiency of waste-incineration power have been developed. The first involves using more heat-resistant materials for the steam pipes in the plants. One incinerator in Saitama Prefecture that has been generating electricity since 1995 has been able to hike its efficiency to 21% by replacing its pipes with chlorine-resistant stainless steel conduits and boosting steam temperature to 380 degrees. The plant is now able to generate 720 kilowatts per ton of trash, as opposed to the 200 to 300 kilowatts that a normal incinerator is able to obtain.
The second technological development is a dual generating system involving both gas turbines and trash incineration. Turbines are powered by natural gas to produce electricity; the exhaust from the turbines, which reaches temperatures from 500 to 600 degrees, is then used to further heat the steam produced by the trash incinerator to about 400 degrees. This type of power plant, called a "super waste incinerator," has been generating electricity on a trial basis since the end of last year in both Gunma Prefecture and in the city of Sakai, Osaka Prefecture. Another "super" plant should go on line in Kitakyushu, Fukuoka Prefecture, in summer 1998. The Gunma dual-system plant is capable of producing 25 megawatts of electricity and has achieved an efficiency rate of over 30%.
These highly efficient waste-incineration power plants consume about 20% to 30% of their generated electricity themselves; the remainder is sold back to utility companies. One plant in Saitama Prefecture uses one-third of the 24 megawatts it generates and earns 1.3 billion yen (11.3 million dollars at 115 yen to the dollar) annually by selling the remaining two-thirds of the electricity. This is quite a difference from before the switch to high-efficiency equipment, when the plant paid 180 million yen (1.6 million dollars) each year for the power it needed.
Next on the drawing board are ways to reduce the cost of plant construction and make it easier to store electricity produced overnight until it can be used. As these new technologies are developed, the number of waste incinerators producing electricity is sure to leap.

power generation

Hey Larry here,
If you’re looking for the best way to generate power at home, then I’m glad you’ve found this website and I strongly suggest you keep reading…
Because this is my uncensored home power generation story. The good, the bad, what stuff did not work and finally the one thing that did end up helping me achieve my main goal of home power generation.
Click here to see the website that showed me how to generate power at home.
I was tired of paying the high rates my energy company was demanding. Demanding because if I refuse to pay then they will shut off my power. I grew tired of being tied down to my local electric company and decided to do something productive about it.
I tried changing electric companies and was able to get a better rate. However, it’s not really much better otherwise. You are still locked into them for power supply and in most cases you are required to sign in for a 6 month or 12 month contract. I have heard of people “cheating” their power company but of course that is not something that I could do. I had also checked with some local retailers and learned that a basic solar installation could cost over $20,000 dollars. Can you beleive that? At this point, I just wasn’t sure what other options I had.
And then it happened. I stumbled across a “how to” product called Earth4Energy which really blew my mind. I hadn’t really thought much about home power generation and how that could solve my main problem of being locked in with the local electric company. This product actually showed me where to get the materials and how to build it all myself saving me a ton. It was actually kind of fun too! The only thing I didn’t really like about the Earth4Energy product was that the videos were kind of large and on my slow connection it took a while to download them all. I hope you found this useful and are thinking about looking into home power generation as it’s the way of the future. You can check it out:

electrical equipment

types of omputer virsus

Viruses can be catagorized in more than one way.  For example, they can be catagorized by their primary function and propagation method as follows:
Trojan horse--enters a system disquised as something else
Worm--propagates on its own by a variety of means including hijacking email accounts, user ids, file transfer programs, etc.
Bomb--doesn't propagate itself at all, is placed by a human or another program and activated by a trigger such as time or event. Usually does something unpleasant when it goes off.
Port Scanner--hides on a system and scans the surrounding environment for IP addresses and open ports that it then makes available to other malicious code or individuals.

The way viruses are usually catagorized however, is by what they do as follows:
Boot Virus--infects the boot sector of disk storage  (Form, Disk Killer, Michelangelo)
Program Virus--infects executable programs (Sunday, Cascade )
Multipartite Virus--combination of the first two (Invader, Flip, Tequila)
Stealth Virus--able to avoid detection by a variety of means such as removing itself from the system registry, masqarading as a system file, etc. (Frodo, Joshi, Whale)
Parasitic Virus--embeds itself into another file or program such that the orginal file is still viable (Jerusalem)
Polymorphic Virus--changes its code structure to avoid detection and removal, mutates (Stimulate, Cascade, Phoenix, Evil)
Macro Virus--exploits the macro language of a program like MSWord or MSExcel for malicious purpose (DMV, Nuclear, Word Concept)
Hope this is helpful

Computer Networking

Computer Network
A computer network is a group of computers that are connected to each other for the purpose of communication. Computer networking is the engineering discipline concerned with communication between computer systems or devices. Networking, routers, routing protocols, and networking over the public Internet have their specifications defined in documents called RFCs (Request for Comment).
A computer network allows sharing of resources and information among devices connected to the network. The Advanced Research Projects Agency (ARPA) funded the design of the “Advanced Research Projects Agency Network” (ARPANET) for the United States Department of Defense. It was the first operational computer network in the world. Development of the network began in 1969, based on designs developed during the 1960s. For a history see ARPANET, the first network. Computer networking is sometimes considered a sub-discipline of telecommunications, computer science, information technology and/or computer engineering. Computer networks rely heavily upon the theoretical and practical application of these scientific and engineering disciplines.

Types of Computer Networks
The most common types of Computer Networks are:
• LAN
• MAN
• WAN


Local Area Network is usually a small network constrained to a small geographic area. An example of a LAN would be a computer network within a building.

LAN (Local Area Network)

LAN Design
Ethernet
When we talk about a LAN, Ethernet is the most popular physical layer LAN technology today. Its standard is

Local Area Network

defined by the Institute for Electrical and Electronic Engineers as IEEE Standard 802.3, but was originally created by Digital Intel Xerox (DIX). According to IEEE, information for configuring an Ethernet as well as specifying how elements in an Ethernet network interact with one another is clearly defined in 802.3.

For half-duplex Ethernet 10BaseT topologies, data transmissions occur in one direction at a time, leading to frequent collisions and data retransmission. In contrast, full-duplex devices use separate circuits for transmitting and receiving data and as a result, collisions are largely avoided. A collision is when two nodes are trying to send data at the same time. On an Ethernet network, the node will stop sending when it detects a collision, and will wait for a random amount of time before attempting to resend, known as a jam signal. Also, with full-duplex transmissions the available bandwidth is effectively doubled, as we are using both directions simultaneously. You MUST remember: to enjoy full-duplex transmission, we need a switch port, not a hub, and NICs that are capable of handling full duplex. Ethernets media access control method is called Carrier sense multiple access/ collision dectect (CSMA/CD). Because of Ethernets collision habits it is also known as the best effort delivery system. Ethernet cannot carry data over 1518 bytes, anything over that is broken down into. Travel size packets.
Fast Ethernet
For networks that need higher transmission speeds, there is the Fast Ethernet standard called IEEE 802.3u that raises the Ethernet speed limit to 100 Mbps! Of course, we need new cabling to support this high speed. In 10BaseT network we use Cat3 cable, but in 100BaseT network we need Cat 5 cables. The three types of Fast Ethernet standards are 100BASE-TX for use with level 5 UTP cable, 100BASE-FX for use with fiber-optic cable, and 100BASE-T4 which utilizes an extra two wires for use with level 3 UTP cable.
Gigabit Ethernet
Gigabit Ethernet is an emerging technology that will provide transmission speeds of 1000mbps. It is defined by the IEEE standard The 1000BASE-X (IEEE 802.3z). Just like all other 802.3 transmission types, it uses Ethernet frame format, full-duplex and media access control technology.

Token Ring
Token Ring is an older standard that isn’t very widely used anymore as most have migrated to some form of Ethernet or other advanced technology. Ring topologies can have transmission rates of either 4 or 16mbps. Token passing is the access method used by token ring networks, whereby, a 3bit packet called a token is passed around the network. A computer that wishes to transmit must wait until it can take control of the token, allowing only one computer to transmit at a time. This method of communication aims to prevent collisions. Token Ring networks use multistation access units (MSAUs) instead of hubs on an Ethernet network.

MAN (Metropolitan Area Network)

A metropolitan area network (MAN) is a network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN). It might cover a

Metropolitan Area Network

group of nearby corporate offices or a city and might be either private or public. A MAN can support both data and voice, and might even be related to the local cable television network. A MAN just has one or two cables and does not contain switching elements, which shunt packets over one of several potential output lines. Not having to switch simplifies the design.
In simple Language we can define MAN as
A metropolitan area network (MAN) is a network that connects two or more local area networks or campus area networks together but does not extend beyond the boundaries of the immediate town/city. Routers, switches and hubs are connected to create a metropolitan area network. Such networks are being implemented by innovative techniques, such as running optical fibre through subway tunnels. A popular example of a MAN is SMDS. The term is applied to the interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network). It is also used to mean the interconnection of several local area networks by bridging them with backbone lines. The latter usage is also sometimes referred to as a campus network.
The main reason for even distinguishing MANs as a special category is that a standard has been adopted for them, and this standard is now being implemented. It is called DQDB (Distributed Queue Dual Bus) for people who prefer numbers to letters, 802.6. DQDB consists of two unidirection buses (cables) to which all the computers are connected. Each bus has a head-end, a device that initiates transmission activity. Traffic that is destined for a computer to the “right” of the sender uses the “upper” bus. Traffic to the “left” uses the “lower” one.
Examples of metropolitan area networks of various sizes can be found in the metropolitan areas of London, England; Lodz, Poland; and Geneva, Switzerland. Large universities also sometimes use the term to describe their networks. A recent trend is the installation of wireless MANs.

WAN (Wide Area Network)

The term Wide Area Network (WAN) usually refers to a network which covers a large geographical area, and use communications circuits to

Wide Area Network

connect the intermediate nodes. WANs often connect multiple smaller networks, such as local area networks (LANs) or metro area networks (MANs). The world’s most popular WAN is the Internet. Some segments of the Internet, like VPN-based extranets, are also WANs in themselves. Finally, many WANs are corporate or research networks that utilize leased lines.
Numerous WANs have been constructed, including public packet networks, large corporate networks, military networks, banking networks, stock brokerage networks, and airline reservation networks. Some WANs are very extensive, spanning the globe, but most do not provide true global coverage. Organisations supporting WANs using the Internet Protocol are known as Network Service Providers (NSPs). These form the core of the Internet.

WAN Protocols
In general, there are three broad types of WAN access technology. With Leased Lines, we have point-to-point dedicated connection that uses pre-established WAN path provided by the ISP. With Circuit Switching such as ISDN, a dedicated circuit path exist only for the duration of the call. Compare to traditional phone service, ISDN is more reliable and is faster. With Packet Switching, all network devices share a single point-to-point link to transport packets across the carrier network – this is known as virtual circuits.

When we talk about Customer premises equipment(CPE), we are referring to devices physically located at the subscriber?s location. Demarcation is the place where the CPE ends and the local loop begins. A Central Office(CO) has switching facility that provides point of presence for its service. Data Terminal Equipment(DTE) are devices where the switching application resides, and Date Circuit-terminating Equipment(DCE) are devices that convert user data from the DTE into the appropriate WAN protocol. A router is a DTE, while a DSU/CSU device or modem are often being referred to as DCEs.

• Peer to Peer - A peer to peer network is one in which lacks a dedicated server and every computer acts as both a client and a server. This is a good networking solution when there are 10 or less users that are in close proximity to each other. A peer to peer network can be a security nightmare, because the people setting permissions for shared resources will be users rather than administrators and the right people may not have access to the right resources. More importantly the wrong people may have access to the wrong resources, thus, this is only recommended in situations where security is not an issue.

Some more types of Networks

• Client/Server - This type of network is designed to support a large number of users and uses dedicated server/s to accomplish this. Clients log in to the server/s in order to run applications or obtain files. Security and permissions can be managed by 1 or more administrators which cuts down on network users medling with things that they shouldn’t be. This type of network also allows for convenient backup services, reduces network traffic and provides a host of other services that comes with the network operating system(NOS).
• Centralized - This is also a client/server based model that is most often seen in UNIX environments, but the clients are “dumb terminals”. This means that the client may not have a floppy drive, hard disk or CDROM and all applications and processing occur on the server/s. As you can imagine, this requires fast and expensive server/s. Security is very high on this type of network.

Peer to Peer Network

Client/Server Network

Electrical machine

Losses in a D.C. Motor

Saturday, September 19th, 2009

The losses occurring in a d.c. motor are the same as in a d.c. generator  (i) copper losses (ii) Iron losses or magnetic losses (iii) mechanical losses As in a generator, these losses cause (a) an increase of machine temperature and (b) reduction in the efficiency of the d.c. motor. The following points may be noted: (i) Apart from armature Cu loss, field Cu loss and brush contact loss, Cu losses also occur in interpoles (commutating poles) and compensating windings. Since these windings carry armature current (Ia), Loss in interpole winding = Ia 2× Resistance of interpole winding Loss in compensating winding = Ia 2× Resistance of compensating winding (ii) Since d.c. machines (generators or motors) are generally operated at constant flux density and constant speed, the iron losses read more
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Posted in DC Motor, Direct Current Machines, Electrical Machines | 1 Comment »

Commutation in D.C. Motors

Friday, September 18th, 2009

Since the armature of a motor is the same as that of a generator, the current from the supply line must divide and pass through the paths of the armature windings. In order to produce unidirectional force (or torque) on the armature conductors of a motor, the conductors under any pole must carry the current in the same direction at all times. This is illustrated in Fig. (4.10). In this case, the current flows away from the observer in the conductors under the N-pole and towards the observer in the conductors under the S-pole. Therefore, when a conductor moves from the influence of N-pole to that of S-pole, the direction of current in the conductor must be reversed. This is termed as commutation. The function of the commutator and the brush gear in a d.c. motor is to cause the reversal read more
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Posted in DC Motor, Direct Current Machines, Electrical Machines | 1 Comment »

Armature Reaction in D.C. Motors

Wednesday, September 16th, 2009

As in a d.c. generator, armature reaction also occurs in a d.c. motor. This is expected because when current flows through the armature conductors of a d.c. motor, it produces flux (armature flux) which lets on the flux produced by the main poles. For a motor with the same polarity and direction of rotation as is for generator, the direction of armature reaction field is reversed. (i) In a generator, the armature current flows in the direction of the induced e.m.f. (i.e. generated e.m.f. Eg) whereas in a motor, the armature current flows against the induced e.m.f. (i.e. back e.m.f. Eg). Therefore, it should be expected that for the same direction of rotation and field polarity, the armature flux of the motor will be in the opposite direction to that of the generator. Hence instead of read more
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Posted in DC Motor, Electrical Machines | No Comments »

Torque and Speed of a D.C. Motor

Wednesday, September 16th, 2009

For any motor, the torque and speed are very important factors. When the torque increases, the speed of a motor increases and vice-versa. We have seen that for a d.c. motor; N = K (V- IaRa)/ Ф = K Eb/ Ф…………………………………………….(i) Ta α ФIa…………………………………………………………………………(ii) If the flux decreases, from Eq.(i), the motor speed increases but from Eq.(ii) the motor torque decreases. This is not possible because the increase in motor speed must be the result of increased torque. Indeed, it is so in this case. When the flux decreases read more
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Posted in DC Motor, Direct Current Machines, Electrical Machines | No Comments »

Speed of a D.C. Motor

Monday, September 14th, 2009

Eb = V-IaRa But Eb=PФZN/60A PФZN/60A  = V- IaRa Or  N = (V- IaRa)/ Ф ×  60A/ PZ Or N = K (V- IaRa)/ Ф But         V- IaRa = Ea Therefore N= K Eb/ Ф Or N α Eb/ Ф Therefore, in a d.c. motor, speed is directly proportional to back e.m.f. Eb and inversely proportional to flux per pole Ф. Speed Relations If a d.c. motor has initial values of speed, flux per pole and back e.m.f. as N1 ,Ф1 and Eb1 respectively and the corresponding final values are N2 ,Ф2 and Eb2 then, N1 α Eb1/ Ф1 and N2 α Eb2/ Ф2 Therefore N2/ N1 = (Eb2/ Eb1) ×( Ф1 / Ф2) (i) For a shunt motor, flux practically remains constant so that Ф1 = Ф2. therefore  N2/ N1 = Eb2/ Eb1 (ii) For a series motor, Ф α Ia prior to saturation. therefore N2/ N1 = (Eb2/ Eb1) × (Ia1/Ia2) where Ia1 = initial read more
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types of computer users

I remember my first computer teacher relaying this very important piece of wisdom. “There are two types of computer users – those who have lost their data and those about to.”
Disaster can strike at any minute – a web server getting fried or even a power surge in your own system. In one second, much or even all you may have worked on may disappear; unless of course you regularly back up. Backing up is something we all know we should be doing, but more often than not we don’t do it enough – or at all.
I was speaking to someone tonight who is paying the price for not backing up. A few hours downtime already while he struggles to breathe life into what appears to be a dodgy hard drive. If the drive is cactus, the only option left is data recovery. This will mean a couple more days downtime and the cost for the recovery service will be anywhere from $500 – $2000. That sounds pretty steep but as one technician said to me a while ago, “Well, how much is your data worth?”
In regards to your web sites, don’t trust your web host to maintain backups. It doesn’t matter what type of great backup scheme they have in place or what whizz-bang equipment they use to help ensure reliability and recovery in a disaster; stuff happens – and their terms of service will usually have that disclaimer as well.
Backing up your online and offline data can be a pain; it’s certainly one of the more mundane tasks of running an online business; but ask yourself – where would you be if your hard drive died this minute and you had no backup

working of thyrister

types of moniters

Different types of computer monitor
As the technology has improved and the prices have come down, LCD (Liquid Crystal Display) monitors have rapidly been replacing CRT (Cathode Ray Tube) monitors on desktops around the world. ComputerWorld first reported that LCD sales would surpass CRT sales for the first time in 2003, a lead that it didn't hold for good.
But according to DisplaySearch, a flat panel display market research and consulting company, the sales of LCD monitors regained the lead over CRT sales in the third quarter of 2004, a lead that it should eventually hold for good.
 
The question is why choose LCD over CRT?

There are several pros and cons to consider, and the few items listed below will be considered in this Geek Tip.
• Price
• Size
• Image Quality
• Energy Consumption
• Personal Comfort
• Response Time

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Price
The price of LCD monitors is much lower than a few years (or even months) ago, but still far exceeds the price of a comparable CRT monitor. For example, I spent about $600 (US) on a Viewsonic VA-720 17" LCD monitor in early 2003, and see that the same model now sells for less than $300. A significant price drop, but in comparison a 17" Viewsonic CRT monitor can currently be purchased for less than $100. The ratio of prices may have narrowed from about 5:1 to 3:1, but the aging technology behind CRTs still allows it to hold the lead.
You can't even compare prices of CRTs to LCDs in CompGeeks monitor section as they are right in step with the sales information provided above, and now only carry LCD monitors. Prices vary, even among LCD monitors of the same screen size, so there has to be something more to it than price.

Size
One reason that LCDs have gained in popularity is because of their small foot print. The overall size and weight of CRT monitors far exceeds that of LCD monitors. CRTs share the same image processing technology with tube televisions, and therefore share the same bulky style of housing.
Desktop real estate is precious, and an LCD will require only a small fraction of the depth that a CRT would require. And if there isn't even enough room on your desk for a slim LCD monitor, the low weight makes them perfectly adaptable to be hung on the wall, or off of a radial arm mount, such as this one from

Image Quality
Image quality is generally considered to be better on an LCD, as each pixel is generated by a specific set of transistors in the screen, which produces a crisp image. But some features that fall under the general heading of image quality might not favor an LCD, including viewing angle, brightness, and contrast.
Early LCD monitors had a fairly narrow viewing angle that made clearly seeing the screen from anywhere but directly in front of it difficult. This has improved greatly, but still doesn't quite rival the viewing angle of CRTs which provide the same picture quality regardless of the angle. A monitor with a maximum vertical viewing angle of 120 degrees should not be hard to find at this point, with many monitors now being able to provide an even greater angle.
Brightness is an area that LCD monitors may have the edge over CRTs, but it varies widely from unit to unit. The standard measure for brightness is referred to as "nits", which have units of cd/m2 (candelas per square meter), where a higher number is better.
Contrast is similar to brightness in the fact that it varies widely from unit to unit, and is a specification where a higher number is desired. The contrast is represented as a ratio, where higher numbers imply that bright colors can be displayed next to dark colors without them appearing washed out. Monitors with lower numbers in the ratio may also result in dark shades being displayed as just black, and any detail in these areas may be lost. As a point of reference, CRT monitors may have contrast ratios around 700:1.
Energy Consumption
LCD monitors definitely hold the edge over CRT monitors when it comes to being energy efficient. The huge tube in a CRT monitor is the source of most of its energy consumption, and a comparably sized LCD may use just a fraction of the electricity.
For example a 19" LCD monitor consumes 48 Watts during normal operation, which is less than your typical light bulb. In contrast, a 19" CRT may draw up to 160 Watts.
Therefore the fraction of electricity used in this case is 3/10, and could translate to noticeable savings on your electricity bill.
Personal Health and Comfort
The main benefit that LCDs have when it comes to comfort is the reduced strain on your eyes. The reduced glare on the screen's surface, and the elimination of a typical CRT's "refresh", can prevent your eyes from getting tired from extended use.
A CRT monitor redraws the image on the entire screen as it refreshes, whereas an LCD monitor only changes the necessary pixels during a refresh.
There may also be the unquantifiable effect of reduced electromagnetic emissions on LCD monitors. The exact impact of electromagnetic emissions may not be fully understood, but in general less is considered to better, as addressed in this article.
And, your back may also appreciate an LCD when it comes time to move, as the example above shows a 19" LCD monitor weighs about ¼ as much as its CRT counterpart.
check out different types of computer monitor

Response Time
<>The transistors that create the image on a TFT LCD can be a bottleneck to its performance, especially in fast paced 3D games where speed is critical. Related to the different approach taken with screen refreshes, the amount of time it takes the pixels to change in order to display the new image is referred to as the response time.
If the response time is too slow, one may experience blurred images or ghost effects where the previous image is still slightly visible with the new image.
LCD monitor response times have greatly improved over the past few years, and many LCDs are now fast enough to consider for serious 3D gaming use, but specifications still vary from unit to unit.
A few years ago a typical response time on an LCD monitor may have been anywhere from 30 to 50 milliseconds, and today these numbers can get down into the single digits, with anything 25 milliseconds or less being quite common (lower is definitely better)
Final Words
In addition to some of the positives mentioned, many LCD monitors now incorporate other features to make them more practical and even fun. LCD monitors can now be found with integrated USB hubs, stereo speakers, and TV tuners
LCD monitors will continue to replace CRTs as they become less expensive and the many benefits are realized by consumers, but CRTs won't disappear all together as many situations require the performance that LCDs currently can't provide.

types of the computer

Analog Computers: These are almost extinct today. These are different from a digital computer because an analog computer can perform several mathematical operations simultaneously. It uses continuous variables for mathematical operations and utilizes mechanical or electrical energy.

Hybrid Computers: These computers are a combination of both digital and analog computers. In this type of computers, the digital segments perform process control by conversion of analog signals to digital ones.

Following are some of the other important types of computers.

Mainframe Computers: Large organizations use mainframes for highly critical applications such as bulk data processing and ERP. Most of the mainframe computers have the capacities to host multiple operating systems and operate as a number of virtual machines and can thus substitute for several small servers.

Microcomputers: A computer with a microprocessor and its central processing unit is known as a microcomputer. They do not occupy space as much as mainframes. When supplemented with a keyboard and a mouse, microcomputers can be called as personal computers. A monitor, a keyboard and other similar input output devices, computer memory in the form of RAM and a power supply unit come packaged in a microcomputer. These computers can fit on desks or tables and serve as the best choices for single-user tasks.

Personal computers come in a variety of forms such as desktops, laptops and personal digital assistants. Let us look at each of these types of computers.

Desktops: A desktop is intended to be used on a single location. The spare parts of a desktop computer are readily available at relative lower costs. Power consumption is not as critical as that in laptops. Desktops are widely popular for daily use in workplaces and households.

Laptops: Similar in operation to desktops, laptop computers are miniaturized and optimized for mobile use. Laptops run on a single battery or an external adapter that charges the computer batteries. They are enabled with an inbuilt keyboard, touch pad acting as a mouse and a liquid crystal display. Its portability and capacity to operate on battery power have served as a boon for mobile users.

Personal Digital Assistants (PDAs): It is a handheld computer and popularly known as a palmtop. It has a touch screen and a memory card for storage of data. PDAs can also be effectively used as portable audio players, web browsers and smart phones. Most of them can access the Internet by means of Bluetooth or Wi-Fi communication.

Minicomputers: In terms of size and processing capacity, minicomputers lie in between mainframes and microcomputers. Minicomputers are also called mid-range systems or workstations. The term began to be popularly used in the 1960s to refer to relatively smaller third generation computers. They took up the space that would be needed for a refrigerator or two and used transistor and core memory technologies. The 12-bit PDP-8 minicomputer of the Digital Equipment Corporation was the first successful minicomputer.

Supercomputers: The highly calculation-intensive tasks can be effectively performed by means of supercomputers. Quantum physics, mechanics, weather forecasting, molecular theory are best studied by means of supercomputers. Their ability of parallel processing and their well-designed memory hierarchy give the supercomputers, large transaction processing powers.
Wearable Computers: A record-setting step in the evolution of computers was the creation of wearable computers. These computers can be worn on the body and are often used in the study of behavior modeling and human health. Military and health professionals have incorporated wearable computers into their daily routine, as a part of such studies. When the users’ hands and sensory organs are engaged in other activities, wearable computers are of great help in tracking human actions. Wearable computers are consistently in operation as they do not have to be turned on and off and are constantly interacting with the user.

Hydroelectric Power generation

Hydroelectric power: How it works

So just how do we get electricity from water? Actually, hydroelectric and coal-fired power plants produce electricity in a similar way. In both cases a power source is used to turn a propeller-like piece called a turbine, which then turns a metal shaft in an electric generator, which is the motor that produces electricity. A coal-fired power plant uses steam to turn the turbine blades; whereas a hydroelectric plant uses falling water to turn the turbine. The results are the same.
Take a look at this diagram (courtesy of the Tennessee Valley Authority) of a hydroelectric power plant to see the details:

The theory is to build a dam on a large river that has a large drop in elevation (there are not many hydroelectric plants in Kansas or Florida). The dam stores lots of water behind it in the reservoir. Near the bottom of the dam wall there is the water intake. Gravity causes it to fall through the penstock inside the dam. At the end of the penstock there is a turbine propeller, which is turned by the moving water. The shaft from the turbine goes up into the generator, which produces the power. Power lines are connected to the generator that carry electricity to your home and mine. The water continues past the propeller through the tailrace into the river past the dam. By the way, it is not a good idea to be playing in the water right below a dam when water is released!

This diagram of a hydroelectric generator is courtesy of U.S. Army Corps of Engineers.
As to how this generator works, the Corps of Engineers explains it this way:
"A hydraulic turbine converts the energy of flowing water into mechanical energy. A hydroelectric generator converts this mechanical energy into electricity. The operation of a generator is based on the principles discovered by Faraday. He found that when a magnet is moved past a conductor, it causes electricity to flow. In a large generator, electromagnets are made by circulating direct current through loops of wire wound around stacks of magnetic steel laminations. These are called field poles, and are mounted on the perimeter of the rotor. The rotor is attached to the turbine shaft, and rotates at a fixed speed. When the rotor turns, it causes the field poles (the electromagnets) to move past the conductors mounted in the stator. This, in turn, causes electricity to flow and a voltage to develop at the generator output terminals."

Pumped storage: Reusing water for peak electricity demand

Demand for electricity is not "flat" and constant. Demand goes up and down during the day, and overnight there is less need for electricity in homes, businesses, and other facilities. For example, here in Atlanta, Georgia at 5:00 PM on a hot August weekend day, you can bet there is a huge demand for electricity to run millions of air conditioners! But, 12 hours later at 5:00 AM .... not so much. Hydroelectric plants are more efficient at providing for peak power demands during short periods than are fossil-fuel and nuclear power plants, and one way of doing that is by using "pumped storage", which reuses the same water more than once.
Pumped storage is a method of keeping water in reserve for peak period power demands by pumping water that has already flowed through the turbines back up a storage pool above the powerplant at a time when customer demand for energy is low, such as during the middle of the night. The water is then allowed to flow back through the turbine-generators at times when demand is high and a heavy load is placed on the system.
The reservoir acts much like a battery, storing power in the form of water when demands are low and producing maximum power during daily and seasonal peak periods. An advantage of pumped storage is that hydroelectric generating units are able to start up quickly and make rapid adjustments in output. They operate efficiently when used for one hour or several hours. Because pumped storage reservoirs are relatively small, construction costs are generally low compared with conventional hydropower facilities.

electric power Diagramme

Electrical Power System Block Diagram

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An idea on how to make a starter/generator circuit. When switching to live power, the generator relay will switch on first, then the battery relay will switch to the charger. When going back to battery, it will first switch on, then the generator relay will switch to start. The DC/DC will need to be able to take both of the sources at once. The system defaults to battery/start mode, in case the engine dies in flight.

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soler power energy cycle

Water Cycle Diagram And Water Conservation

By James J Dixon

Water cycle diagram helps one understand the process of rainwater formation and the importance of water conservation. We need to conserve our water to meet the needs of an increasing population. These days of tapped water in urban areas, do not reflect the true needs of people living in rural areas and areas with long periods of drought.
There are areas in our country where it only rains for a short period of the year and the rest of the year is mostly dry. We need to take action to conserve as much water as possible to prevent too much water simply evaporating and disappearing.
You can take measures to use less water. Easy steps include using less water, cut down wasting water by fixing dripping taps and leaky pipes and take measures to reuse water and saving water with a rainwater tank. Remember, water in your water tank, gathered from the rain is water you do not have to pay the water utility. It is free water.
Unless, of course you live in a drought area and water has to be trucked in, to fill your water tank.

A Water Cycle Diagram

I remember the first time I saw a water cycle diagram. I was in middle school, and I had no idea why it was important. I knew vaguely that water changed places frequently. I knew, for example, that it would go up into the air and form clouds, come down as rain, and slowly drain out into the ocean. The significance of this fact was lost on me however.
That is why when I show my students a diagram of the water cycle, I am careful to explain its significance. Nowadays, water cycle diagrams and not just a casual part of the curriculum. They are absolutely crucial to understand.
After all, with global warming as it is, understanding the water cycle is important for the leaders of tomorrow. The water cycle, you see, is one of the most important environmental cycles. Almost everything about our environment is completely dependent on it.

power supply circuit diagramme

500w power invertor

Designed by: Syed Ashad Mustafa Younus
Revised by: Ronnie B. Tabanao

working of transistor

GTO is a special thyristor which can be turned on by a positive gate signal and can be turned off by a neagative signal.Evidently the use of GTO in power electronic circuit eliminates the need of forced commutation circuit because turnoff is achieved by applying a negative circuit.

The two transistor analogy of a GTO

Two transistor analogy of transistor is shown in figure below

When a positive signal is applied,a GTO switches into conduction state like the ordinary thyristor.However in ordinary thyristor the current gains of NPN and PNP transistors are very high so that gate sensitivity for turn on is very high and on state voltage drop is low.However in GTO,the current gai of PNP transistor is low so that turn of fis possible if significant current is drawn from the gate.When a negative gate signal is applied the excess carriers are drawn from the base region of NPN transistor and collector current of PNP is diverted to the gate.Thus the base drive of NPN transistor is removed and this inturn removes the base drive of PNP transistor and turnoff is achieved

thyrister

Thyristor is also called SCR, stands for Semi Conductor 
Rectifier. It is basically a four layer semi conductor 
device like a transistor that is a three layer 
semiconductor device. 

It is generally used as a switch in the power circuit as it 
can only be turned on by providing a pulse at its one of 
the sandwitched layer called Gate, and the pulse is also 
called firing pulse or  triggring pulse. The main advantage 
of this over the transistor is the it can be used into the 
power circuits.

 

A thyristor is a semiconductor device which acts as a 
switch. However, when switched on it can only pass current 
in one direction. It is in fact a switchable diode 
sometimes known as a silicon controlled rectifier. To 
switch alternating current two devices are connected in 
inverse parallel. 

Each device is turned on at the appropriate time by a 
trigger pulse applied to the gate and the device will 
remain on until the instantaneous load current through it 
drops to zero. 

The trigger pulses are generated by a driver - which times 
the pulses to ensure the thyristor unit output is a 
function of the input demand signal (e.g. from a 
controller) in the selected Firing Mode.

Eurotherm thyristor units incorporate the thyristor 
devices, together with the driver and the heatsink which 
dissipates the heat generated by the thyristor devices. 
Many units include internal high speed fuses to protect the 
thyristors from high overload currents. The benefits of 
thyristor units are numerous. They offer a reliable long 
term alternative to electromechanical devices reducing the 
necessity for ongoing maintenance.

Thyristor units are particularly cost effective for fast 
systems, for complex loads involving transformers and/or 
heaters whose resistance changes with temperature or time