lammert - 3:48 pm on Jan 22, 2008 (gmt 0)

The advantage of local servers close to the visitors is not because the current internet isn't fast enough but because nothing can travel faster than light.

Light has a maximum speed of about 300,000 km/sec in vacuum. Through fibers, this is lower, about 200,000 km/sec. Electrical signals traveling through a copper cable are limited at roughly the same speed.

When your server is located in the US and your visitor is located in Europe, the amount of cable in between can be as much as 15,000 km. The response on each request has to travel back which makes the total way to travel 30,000 km for every request. Simple math gives a loopback time of 150 msec, which is quite common for trans-atlantic traffic.

So even with more internet bandwidth, the response will always take a certain amount of time and with the current internet, we are already close to that limit.

Now comes the way browsers handle page rendering. First the HTML page is downloaded and interpreted. All the extra files (images, CSS files, JavaScript files) are downloaded seperately. Each of these requests takes at least 150 msec to fullfill. Browsers can spawn multiple requests at the time, but current browsers are limited to request only two files concurrent from one server, or one JavaScript file.

If, as an example you have one HTML file which calls 4 CSS files, 2 JavaScript files, and 20 images, The browser spawns 15 separate request series (1xHTML, 2 CSS series, 2 JS requests and 10 image series) giving, just because of the speed of light a minimum delay of 2250 msec. I don't count here the extra delay because of browser rendering time, traffic congestion, lost packets etc.