What is Bandwidth?
Bandwidth is the amount of data that is transferred through high-speed lines from the server to your site visitors' computers. When you load a Web page you are downloading data. How this adds up is the same as in the discussion of Web space. A 10KB page can be loaded 102 times before you will have used a single megabyte of bandwidth.
Note: Each file within a page is calculated also. So if your 10KB Web page contained three images of 10KB each, every time the page was visited, 40KB of bandwidth would be used; 10 kilobytes for the page and 30 kilobytes for the images.
By CgiScripts.Net
If designed correctly, a Web site can be very successful and receive many visitors and still use very little bandwidth. ... Some hosts try to say that other hosts will not allow you to be successful if they limit your bandwidth. This is obviously not true. Your success is dependant on how you develop, promote, care for, and remain dedicated to the task at hand. If you care about the success of your Web site, you will educate yourself about what your Web site needs. This includes finding a host that will meet those needs efficiently and honestly. Hosts that promise unlimited bandwidth are either not being honest with you, have hidden restrictions they are hoping you will not notice, or simply are not educated themselves and are possibly risking their businesses on the hope that their clients will not use an enormous amount of bandwidth.
It is simple to calculate how much bandwidth you will need if you have an existing Web site: Check your current usage and evaluate it from there. For a first-timer this might be difficult. Starting out with 2 gigabytes of bandwidth is usually more than enough to allow room to develop and grow. This is usually included in the majority of packages hosts offer. If the host is not offering a minimum of 2 gigabytes of bandwidth, you may want to shop around a bit more.
You want to be sure that your host leaves room for growth in case your site becomes popular and requires more bandwidth. If a site contains an enormous amount of images, message forums, or other various products for download this could cause your bandwidth needs to be higher.
Q. The host I am considering using offers unlimited (or limited) hits, transfers, or pages views. Is this same as bandwidth?
A. A host that claims to offer a certain amount of hits, transfers, or page views either lacks knowledge about the Web-hosting business or assumes you are not smart enough to know what bandwidth is. A hit or transfer means someone has downloaded a file from your Web site. (Each page and image downloaded counts as a hit. So using the example above, when a visitor views a page with three photos on it, the server would register four hits.) A page view means someone has visited your Web page.
The host is in fact referring to bandwidth when they make this offer. The flaw in this offer is that there is no way for the host to know what size each of your files will be. Therefore, there is no way for them to predict how many hits, transfers, or page views they will be able to offer you. It is recommended that you either avoid a host making these claims or question the host to confirm exactly how they calculate a hit, transfer, or page view in terms of bandwidth.
Any Web site that uses more then 15 gigabytes of bandwidth per month should be on what is called a dedicated server. Dedicated servers are servers that host only your site and do not share the resources with other sites. These are more expensive than community hosting, but if you care about your site's success and you are using that much bandwidth, then dedicated is the way to go.
Additional Information (by Ryan Petrello):
Size of Files
The size of the files on your Web site make the most difference in the amount of bandwidth you use. Every character within a file for your Web site contains a certain amount of bytes. These bytes add up into the total size of the file, which is usually in Bytes or Kilobytes. Each time a visitor views a file on your site, the page must be downloaded so that they can view it. This is bandwidth's job.
Number of Visitors
The number of visitors also makes a large difference in bandwidth. For a site with more visitors, more files must be downloaded, consuming more bandwidth. This is why bandwidth costs more; you're basically paying more money to show more people your Web site.
Image Links from OTHER Web sites
There is also something known as "theft of bandwidth." Bandwidth theft becomes a problem when many people link to files and images on someone else's server without permission. There are many people who think its OK to link to graphics or other files on someone else's server so they can use them on their own Web site. Stealing bandwidth is illegal. You can be sued if you are costing someone hundreds of dollars in Internet costs. That said, you can also cost yourself more money if you put a direct link on another site to an image that resides on your Web site. Be aware that every time that site displays your image, it is technically a hit to your Web site, since every time the other Web site displays your banner or image, it must come to your Web site to "get it".
Cache
There are exceptions. If bandwidth were calculated solely on the number of visitors and file sizes, we'd all be doomed. It would simply be too much data transfer and too much money. The purpose of your cache is to keep a record of recently used files, or Web sites. The cache, in a way, remembers a Web site for you, and when it's loaded a second or third time, it doesn't take up nearly as much bandwidth.
Someone Has to Pay
While the price is getting lower, bandwidth is still very expensive, especially for larger sites. For this reason, it's not very surprisingly when large Web communities simply shut down out of the blue. You've probably seen it before. Most of these communities are run on the developers' money, and when visits continue to increase, it comes to a point where the developers can no longer afford to keep the site alive. They begin asking their visitors for financial support. And granted, some give. But usually not enough. They have no other option but to shut down.
Take the Advantage
With all this fuss about bandwidth, you'd think some people would stop and think about it for a second. The idea's simple. It's expensive. You pay money for it when it's expensive. So, to pay less money for it, you make it less expensive. How? Well, unless you want hate mail, you surely can't control the flow of your visitors. You don't have much say in your cache's capabilities either. But you can control the size of your files.
Scripting
Many errors in scripting languages account for lost bandwidth. Whatever language you may be using, whether it's PHP, ASP, Perl, or Coldfusion, the resulting bandwidth is determined by the processes the script does, and how much resources it takes to complete. Basically, the more quickly and efficiently your script runs, the less bandwidth you'll be using. To stay within these rules, make sure not to add pointless loops here and there, don't output more information than you need to, and never make more than one connection to the same database.
Nomenclature
If you think about it a bit more, it's not just the contents of files that are being accessed. The server also needs to know their names. For this reason, it's much wiser to create a file named index.html rather than mymainwebsitepage.html. That's 12 more characters, which can and will add up on larger sites. This even holds true to folder names. For this very reason, you'll find many sites that, rather than putting their CSS files into a folder called /css, assign only one letter to their folders, such as /c. Why waste the money if you don't have to?
