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DNS in a nutshell
As I said above, DNS is a translation service from computer readable names, to human readable names. The theory is similar to a phone book, or directory assistance, which translate phone numbers to names. The DNS system is distributed across the whole Internet, virtually every Internet provider has two or more DNS servers, most hosting companies do as well, and a lot of large businesses, ie Microsoft, Dell, HP all have their own servers. (of course, having 30,000+ employees, they probably have their own directory assistance too).
Every single person on the Internet uses DNS, 99% of them without even knowing. Every time you go to a website, you do a search of the DNS system to find the location of the site. Every time you send an email, your ISP's mail server does a DNS search to find the mail server for that domain. As I said, DNS works on a distributed basis, no one server holds the records for every single domain. There are a lucky 13 master servers, that contain a list of which DNS servers handle which domains, when you look for a domain that your ISP's DNS server does not know, it asks the master servers, which DNS server does know about this domain, then it asks that DNS server for the information it needs, before passing it back to you.
Changing DNS Servers
When you change hosting providers, the normal procedure is to also change your domain's delegation to the new hosting providers DNS servers. This procedure, known as redelegation, is best, as it means one company handles everything for you, and if they make a change to the location of your website, for instance moving it onto a faster server, they can also update the DNS records straight away, so no one notices. To find out who your domain is delegated to, you need to do a ''whois search''. A whois search will not show you where your website is, but it will show you which DNS servers know where it is. Customers of Anchor should always see '''ns1.anchor.net.au''' and '''ns2.anchor.net.au''' in their whois information. If your domain is currently with another company, and you need to bring it to Anchor, you need to change that information. Generally, this is done through a web page of the company that you registered the domain with, it is a simple change.
Once the change is made, depending on the type of domain, it can take up to 3 days for the rest of the Internet to notice you have moved. (The same as when you move house, it can take quite a while for other people to realize). The reason for this is explained in the next paragraph. Suffice to say, for a period of 3 days, some people will see the new site, some people will still see the old one. Some email will go to the new server, some will go to the old server. This is avoidable through careful planning, and a week long changeover.
Buzzwords & Geek words, translated!
Often when talking about DNS, the words (and abbreviations), '''TTL''', '''Cache''' and '''Propagation''' come up, but what do they mean? In plain English, the DNS server responsible for your domain has a file with all the information about your domain in it, and when another DNS needs information about your domain it is pulled from this file, along with a TTL value. TTL stands for '''Time To Live''', and it is the maximum time a foreign DNS server can store this information locally, without asking if it has changed (the process known as caching). When you redelegate your domain from one DNS server to another, the amount of time it takes depends on the TTL value in the old server. If this value is high, which it generally is (around the 1 day mark) then any DNS server that has requested information on your domain in the past 24hrs will still see the old records; once the TTL period expires the servers will then see the new details.
Additionally for '''.com, .net, .org''' domains, no server will see the change until the DNS system reloads at midnight, USA time, whilst the '''.au''' domains are updated instantly. This process of waiting for all the Internet to see your move is called propagation. As I said above, there is a way to speed up the process, and that is to redelegate a week early with your new hosting company copying the old records, with a very low TTL, (ten minutes or so), and then when you are ready for the website and email to go to the new server, changing them on the new DNS server. This means the whole Internet will see the change in 10 minutes, regardless of the domain name (note, some ISP's do not confirm to the standard for DNS caching, and may not update instantly).
So what does a domain record look like
@ IN SOA ns1.anchor.net.au. hostmaster.anchor.net.au. (
2004030401 ; Serial
28800 ; Refresh
14400 ; Retry
3600000 ; Expire
86400 ) ; Minimum
@ IN NS ns1.anchor.net.au.
IN NS ns2.anchor.net.au.
IN MX 50 smtp1.anchor.net.au.
IN MX 100 smtp2.anchor.net.au.
IN A 202.4.234.122
smtp IN A 203.98.94.10
www IN CNAME @
ftp IN CNAME @
mail IN CNAME smtp
pop IN CNAME smtp
pop3 IN CNAME smtp
That looks scary! What does it all mean?
Lets breakdown the file one line at a time
@ IN SOA ns1.anchor.net.au. hostmaster.anchor.net.au. (
This line, the Start of Authority, states that ns1.anchor.net.au is the domain server responsible for your domain, and that
hostmaster@anchor.net.au is the contact for this server
Skip the next 4 lines: '''Expire, Retry, Maximum and Serial''', as these are not important in this situation
86400 ) ; Minimum
The value of minimum is the TTL, ie the length of time, other servers can cache the information for your domain
@ IN NS ns1.anchor.net.au.
The third column on this line, NS, means nameserver, this line means that your server is listed in ns1.anchor.net.au (and below that in ns2.anchor.net.au). NS lines give a list of all the nameservers responsible for your domain.
IN MX 50 smtp1.anchor.net.au.
Again, the column after IN is important, (all your records should say IN), MX stands for Mail eXchange, and MX lines are a list of servers that handle your email, the number after MX is the priority, the lower the number, the higher the priority
IN A 202.4.234.122
On this line, A means Address. All A records are direct translations of names to numbers. If the line starts with a word, that is a host name, ie '''http://www.yourdomain.com.au'''. If it doesn't have a word, it means just '''yourdomainname.com.au'''. If it has a * it means every subdomain of '''yourdomainname.com.au''' that's
available.
mail IN CNAME smtp
The final record type is CNAME, whilst this stands for Canonical Name, it is often easier to think of it phonetically, ie; See-Name. As thats what it means, in this case, the record tells computers looking for mail.yourdomain.com.au to go look for smtp.yourdomain.com.au instead.
Now don't you feel enlightened?
Do I have to have this? It all seems so complicated
If you want people to see your website, and email you, you must have DNS records. It is unavoidable. However as I said at the start of this article, you only need to have an understanding of the top level of the system, ie, when I redelegate, it takes 3 days, my email will be scattered. You do not need to understand how the entire system works, that is the job of your DNS administrator (often called hostmaster), who is typically your web hosting company.
Can I do this myself?
If you have a static IP address and a permanent Internet connection you can host your own DNS, and if that doesn't make any sense to you, you are probably better off letting someone else handle it. You may notice in a whois search that most domains have 2 DNS servers listed, and some have up to 10. This is for redundancy: if one server dies, but the others are still working, then your website and email are unaffected; but if you only have one server, and it goes down for whatever reason, then your email and website are offline too.
The term IGBT is an acronym for Insulated Gate Bipolar Transistor. It can be thought of as a Transistor with a MOSFET front end. It has three terminals (or leads) labeled Gate, Collector and Emitter. Some IGBT's have a built in protection diode. This diode is connected across the Collector and Emitter terminals. It is added for transient voltage protection when the IGBT is switching Inductive loads.
When these devices are considered 'suspect' it is necessary to validate their operation through a functional test procedure. One of two methods can be used:
The first test method will validate the condition of the protection diode, and the resistance of the Collector and Emitter terminals. It is not a definitive test, but will find 80% of all faulty devices. This is due to the fact that most faulty IGBT's show a low resistance or short across the Collector and Emitter terminals when the device is stressed.
To perform this test will require a DVM (Digital-Volt-Meter). Set the DVM to the Diode Test position, and confirm that the device tests as follows:
Attach the Red Lead of the DVM to the Collector Terminal and Black Lead to the Emitter Terminal. Confirm an open circuit condition.
Attach the Red Lead of the DVM to the Emitter Terminal and Black Lead to the Collector Terminal. Confirm an open circuit condition (IGBT without a protection diode). If the DVM displays a forward voltage drop of 0.2 to 0.8 VDC it means that the IGBT has a built in protection diode. Both of these results are normal test conditions and are used to confirm whether the IGBT has a protection diode, and if it does, whether it is functional or not.
The second test method will check the IGBT's functionality, by gating the device. To perform this test will require an IGBT Tester. Confirm that the device tests as follows:
Attach the IGBT Tester leads to the Gate, Collector and Emitter Terminals. Confirm that the device Conduction LED is not lit.
Press the Test Button, and confirm that the Conduction LED lights.
Reverse the Collector and Emitter leads. Do not press the Test Button. If the Conduction LED lights the IGBT has a built in protection diode. This is a normal test condition for this type of device. If the Conduction LED does not light then the IGBT does not have a built in protection diode. This is also a normal test condition for this type of device.
It is important to note that Functional test of the IGBT should always be performed when the device is out-of-circuit. In other words, it should be removed from the product and have no other electrical connections in place, other than those outlined in the Test procedure.
E-Commerce and E-Business are two completely different terms but unfortunately they are always used interchangeably by many of us. The reason behind this lies in the meanings of "business" and "commerce" in English language. But there is a difference between e-commerce and e-business. There are many people who understand the subtle differences between the two and there had always been a debate among these two groups about the differences and similarities between e-commerce and e-business. The aim of writing this article is to clearly bring out the differences between the two as both of them are completely different phenomenon.
The differences between the two are as follows:
1. E-Commerce is the subset of E-Business. If you remember the Venn diagram you studied in school then you can very well understand what I am trying to convey. The later one is a very broad concept while the former one is just a small part of it. This relationship will be cleared in the subsequent points.
2. Those activities which essentially involve monetary transactions are termed as "e-commerce". However, e-business is a much broader term. There are many other things besides selling including but not limited to marketing, procurement of raw materials or goods, customer education, looking for suppliers etc.
3. To sell online is e-commerce but to bring and retain customers and educate them online about the product or service is e-business. Having a website to do it is not sufficient. But, having a professionally built website loaded with latest technologies to capture the attention of the visitor and win his/her appreciation is required. When money is involved then the first thing which user looks for is safety and security of his/her money. Having a website laden with such qualities is important.
4. When Dell sell computers, laptops, monitors, printers, accessories etc online then it is not engaged in e-commerce but e-business. Let me tell you how. When a visitor comes on the website, the first thing he see is website design and navigation as well as those things which are going to help him find what he is looking for and if he directly lands on the page he was looking for, he looks for the information related to it. The information provided should be appealing and clear maximum doubts of the visitor so as to convert him in a client. Till now no money has been exchanged nor been talked about. So, was this e-commerce? No, it is e-business which guides the visitor.
5. E-commerce has also been defined as a process covering outward processes that touch customers, suppliers and external partners while e-business covers internal processes such as production, inventory management, product development, risk management, finance etc.
In all, e-commerce can be described as the use of the Internet and the web to transact business. More formally, digitally enabled commercial transactions between and among organizations and individuals. On the other hand, e-business can be described as the digital enablement of transactions and process within a firm, involving information systems under the control of the firm. Moreover, e-business applications turn into e-commerce precisely when an exchange of value occurs.
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There is two types of transformers in the market- linear transformer and switch mode power transformer. The transformers design is different. Sometimes it is just referred as ac transformer. Linear transformer mostly used in radio, project kits, VCD and etc while switch mode transformer can be found in Monitor, Tv, Fax and so on.
A transformer consists of two or more coils wound on the same core. For power transformers, the core material is usually iron. For a radio-frequency transformer, the core material is usually ferrite or air. The basic property of a transformer is to change AC voltage. A transformer cannot change direct current voltage. A step down transformer has a lower AC output voltage at its secondary winding than the AC input voltage to its primary winding. Conversely, a step up transformer has a higher secondary than primary voltage. The transformer laminations or coating of shellac, enamel or varnish is to insulate adjacent turns from shorts between winding. I will not go too details about how transformer work and transformer calculation as you can read more details from most electrical and electronic transformers books.
How to test transformers: Transformer failures are relatively rare in most electronic equipment, compared with other components. If too much current goes through a coil or winding, the winding heats up and can either open up completely, or the insulation between turns of wire can break down, causing the coil to be partly or completely shorted.
Just like a coil, you can check continuity of any primary or secondary transformer winding. The actual value of DC resistance you read is rather meaningless, but at least you will know whether a winding is open. Checking linear transformer is quite straight forward. Apply the ac voltage to the primary winding and expect output voltage at the secondary side. No or low output voltage means the transformer winding has open or shorted winding. Look for any evidence of overheating, such as darkened or blackened areas or a burnt smell.
About how to test a power transformer-it is a little bit complicated. You cannot apply ac voltage to the equipment and expect the desire output at the secondary side without connect to load otherwise over voltage will happen (because you have removed all the secondary load) and will blow the power section which consist of power fet, pwm ic and etc. Switch mode power supply are designed to run with load while linear transformer can be test without load.
The best way to test a switch mode power transformer is first remove it from the board. Check only the primary winding as secondary winding failures are exceedingly rare. How do we know which one is the primary winding? Trace from the big filter cap the positive pin to see where the circuit goes. It will go to one of the pin of the transformer. Then look for the power fet middle pin which is the Drain and it will lead to another pin of the transformer. This two pins is the primary winding of the transformer. Checking the resistance of the primary winding only can reveal whether it is open but it cannot check if it has developed a shorted winding. Only by using a ringer test you will know if it shorted or not. A shorted turn in the primary winding can cause the power section to blow.
The cheapest ringer tester that i came across is Dick Smith LOPT METER or flyback tester. Just connect the probes to the primary winding and the result are instantly seen from the Led bar graph. 4-8 bar represent a good winding, 1-2 bar represent partial short and if the led goes off means there is a heavy short in the winding. Besides checking the transformer it can be use to check B+ COIL, horizontal yoke coil and flyback primary winding and ballast (choke).
The expensive ringer tester is from sencore equipment. Sencore LC102 and LC103C besides checking capacitor it also have the capability to check all kind of winding. Whether it is a low voltage transformer, high voltage transformer, current transformer, pulse transformer, electric transformer, custom transformer this equipment will be able to check and test it.
If you do not wish to invest on this tester you may use a light bulb to check it. Remove one of the primary winding pin and connect a 60 watt light bulb. One end to the circuit while the other to the transformer pin. If the bulb light and didn't goes off suspect a shorted winding and if the light goes off, the winding is ok.
Transformer repair is not easy and it require a good skill to do it. Most of the transformer repairer preferred to rewind bigger winding such as fan, car alternator and starter. Switch mode power transformer is a little bit difficult to rewind because of the small size and low price.
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There's not really a definitive way of how to put video on PSP, but there's a fast and easy way, and this is it. It's not rocket science, but Sony hasn't made putting video on a PSP as simple and straightforward a task as they should have done. But that doesn't mean it can't be simple. Here's how to do it...
You need a memory card with a lot of memory, unless you want to watch tiny little videos that might just fit onto the PSP's default 32Mb memory card. Videos are big files and they take up a lot of space; 32Mb doesn't go far. Go for half a gigabyte at least.
There's lots of places where you can get one. Amazon.com are good. Their SanDisk SDMSPD-512A10 512Mb Pro Duo memory stick is currently less than . Do a search on Amazon for it in the electronics category. If you don't have a Sony product, you'll need a USB cable for the PSP. Again, Amazon have them and they're cheap. Search for a PSP USB Data Cable.
At this point it is assumed that you have access to a computer connected to the Internet. Dialup might work, but you really need a high-speed connection. The good news for any Mac users is that this method works for you as well as for the PC.
OK, here we go...
With the PSP switched off, connect the USB cable to the PSP and to the computer, then switch on the PSP. On the PSP access: Settings > USB Connection. Next, press the X button to boot the PSP on to the computer, where it will appear on the desktop as an untitled volume. Inside the memory card you should see a folder named "PSP" and inside that folder there will be four sub-folders of, "Games", "Music", "Saveddata", and "Photo". You must add a new folder here named, "MP_ROOT" (without the quotes) which must be in the same level as the "PSP" folder. Under the "MP_ROOT" folder add a sub-folder named "100MNV01" -- this is where your MP4 videos and their accompanying thumbnail files (*.THM) will be stored.
Now all you need to do is start downloading MP4 videos. A search for "MP4 videos" in Google in July of 2006 brought up 4,660,000 results, so there's plenty to choose from! Once you have your video(s) downloaded on to your PSP, go to Video > Memory Stick, and there you should see the thumbnail file of the video. To play the video, click on the thumbnail. You can access the screen display modes via the triangle button. There are four to choose from. Now you know how to put videos on PSP, so enjoy your viewing!
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International commerce has rapidly increased as the internet has provided a new and more transparent marketplace for individuals and entities alike to conduct international business and trading activities. Significant changes in the international economic and political landscape have led to uncertainty regarding the direction of foreign exchange rates. This uncertainty leads to volatility and the need for an effective vehicle to hedge foreign exchange rate risk and/or interest rate changes while, at the same time, effectively ensuring a future financial position.
Each entity and/or individual that has exposure to foreign exchange rate risk will have specific foreign exchange hedging needs and this website can not possibly cover every existing foreign exchange hedging situation. Therefore, we will cover the more common reasons that a foreign exchange hedge is placed and show you how to properly hedge foreign exchange rate risk.
Foreign Exchange Rate Risk Exposure - Foreign exchange rate risk exposure is common to virtually all who conduct international business and/or trading. Buying and/or selling of goods or services denominated in foreign currencies can immediately expose you to foreign exchange rate risk. If a firm price is quoted ahead of time for a contract using a foreign exchange rate that is deemed appropriate at the time the quote is given, the foreign exchange rate quote may not necessarily be appropriate at the time of the actual agreement or performance of the contract. Placing a foreign exchange hedge can help to manage this foreign exchange rate risk.
Interest Rate Risk Exposure - Interest rate exposure refers to the interest rate differential between the two countries' currencies in a foreign exchange contract. The interest rate differential is also roughly equal to the "carry" cost paid to hedge a forward or futures contract. As a side note, arbitragers are investors that take advantage when interest rate differentials between the foreign exchange spot rate and either the forward or futures contract are either to high or too low. In simplest terms, an arbitrager may sell when the carry cost he or she can collect is at a premium to the actual carry cost of the contract sold. Conversely, an arbitrager may buy when the carry cost he or she may pay is less than the actual carry cost of the contract bought. Either way, the arbitrager is looking to profit from a small price discrepancy due to interest rate differentials.
Foreign Investment / Stock Exposure - Foreign investing is considered by many investors as a way to either diversify an investment portfolio or seek a larger return on investment(s) in an economy believed to be growing at a faster pace than investment(s) in the respective domestic economy. Investing in foreign stocks automatically exposes the investor to foreign exchange rate risk and speculative risk. For example, an investor buys a particular amount of foreign currency (in exchange for domestic currency) in order to purchase shares of a foreign stock. The investor is now automatically exposed to two separate risks. First, the stock price may go either up or down and the investor is exposed to the speculative stock price risk. Second, the investor is exposed to foreign exchange rate risk because the foreign exchange rate may either appreciate or depreciate from the time the investor first purchased the foreign stock and the time the investor decides to exit the position and repatriates the currency (exchanges the foreign currency back to domestic currency). Therefore, even if a speculative profit is achieved because the foreign stock price rose, the investor could actually net lose money if devaluation of the foreign currency occurred while the investor was holding the foreign stock (and the devaluation amount was greater than the speculative profit). Placing a foreign exchange hedge can help to manage this foreign exchange rate risk.
Hedging Speculative Positions - Foreign currency traders utilize foreign exchange hedging to protect open positions against adverse moves in foreign exchange rates, and placing a foreign exchange hedge can help to manage foreign exchange rate risk. Speculative positions can be hedged via a number of foreign exchange hedging vehicles that can be used either alone or in combination to create entirely new foreign exchange hedging strategies.
Does your Windows 7 boot slow? Wondering how to make Windows 7 boot faster without paying much? Maybe I can help you!
As a latest operating system, Win 7 Integrated more services and applications than any others in the past. With many programs run at startup, Windows 7 will boot slow as a tortoise. These programs not only occupy vast hard drive space, but also lengthen the boot up time greatly. So, more and more users want to know how to make Windows 7 boot faster now.
Of course, you can buy a new computer to make windows 7 faster quickly. But it will cost you much. And no matter how fast a new PC might be, it will get slower over time. So it doesn't mean that you don't need to optimize it again.
The easiest way to make Windows 7 boot faster is to manage your startup items and services. Thinking that if you get more than 50 items and 100 services run at startup, how to make Windows 7 boot faster?
Click Start and input "msconfig" in the Run box. Then point to OK and press. You will see all services and applications that are started automatically when your computer boots. Disenabling some unnecessarily items and re-boot your computer. Your Windows 7 boot up will never be slow again.
But please do it carefully since some services and startup items are very important to Windows. Removing them in error will cause serious problems even system crash. It's not funny at all. So you'd better select some popular tools to do it for you.
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