BT2K's timing tests measure everything--- the result indicates the collective performance of your browser, your system, your connection (e.g. modem), your ISP, the Internet as a whole (including every router or relay along the path your data must travel), and the web server. Each step adds a little delay, or 'latency.' So it's very important to realize that throughput involves a lot more than just what goes on at your end.

It's wise to re-run the BT2K tests at different times and dates to help eliminate transient latency problems that clear themselves up. If you rerun the tests and get similar results each time, you can gain increasing confidence in the results. Conversely, you shouldn't place undue import on a single test run.

HOW THE TESTS WORK:

The BT2K timing tests run by calling "external" JavaScripts--- JavaScripts stored in a location away from the actual BT2K pages you see. The three external JavaScripts are identical and are made up of long, compression-resistant text strings, in which the text has very few characters that repeat (I created the scripts using a random-character generator I wrote). The lack of compressibility means your modem (or ISP) can't artificially reduce the size of the file---every bit will have to be processed. This helps ensure you'll get an accurate reading rather than one artificially inflated by data compression. It also is one reason why the BT2K throughputs may appear lower than what you're used to seeing.

The three external JavaScripts are identical, and of a length that's known literally to the exact number of bits. One script resides on a server in New York, one on the WinMag server farm in California, and one on a server in Florida. By timing how long it takes your browser to receive the script, it's easy to divide the known length by the download time to arrive at a bits/second.

But there's a catch: Calling an external JavaScript means your browser has to contact the remote server, open a connection, access the file, then actually download the file, then close the connection. There's more going on than just downloading the file, and each of those other steps takes a little time.

Think of the difference between smooth highway driving where you can kick in the cruise control and sail along at a steady speed for long distances: Your mileage goes up. Conversely, in stop-and-go driving, your mileage goes way down because it's inherently less efficient.

By loose analogy, there's something similar going on on the Internet. Downloading a large file is analogous to cruising on a high-speed highway. Downloading a short file is more like stop-and-go driving.

Isn't it weird how much goes into even a seemingly simple thing like a throughput test? No wonder I'm going gray! 8-)

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