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Aha, this is one of my favourite subjects
. There are four major things that will dictact your sites performance;
1) Pure Server Grunt. Moderately important, but for the most part can be overcome with careful planning and configuration of the caching system for modules and blocks.
2) Content. Quite important to keep your front page of your site to only the essentials and should ideally be keep at under 100k.
3) HTTP Requests. Very important to keep this as low as possible as each request requires that the server and client
4) Internet connection. Extremely important to have ample available bandwidth for your website. Remember available bandwidth is only equal to that of the slowest link between your server and client. For people still using standard analog modems this is going to be a maximum of 56kbps, which is why it is a very good idea to minimize HTTP requests and content as these have a VERY large influence on how your site performs for these users.
With you Internet connection it is not only available bandwidth you have to consider, but also the connections relativity to the Internet backbone. This can be determined by a trace route. Basically, the closer to the backbone you are the better your site will perform as each hop introduces latency. This isn't so important for local users, but for international users this can have quite an effect on site performance.
THE most useful tool I use for trying to optmise my site is IBM Page Detailer Basic which is a freeware application from IBM (duh!). What it does is connects to your Internet Explorer browser and displays statistics in a graphical form of how long each HTTP request in your website takes to download, and how much data is contained in each. It also shows you things like respnse times which is a great indicator for latency or server lag. Hope this helps a bit
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