[nycphp-talk] So why is Ajax so fast?

Kenneth Downs ken at
Fri Jan 12 09:58:06 EST 2007

We've all seen the amazing results you can get when you start using 
Ajax, they all come down to one thing: speed.

Question is, how is such a speed-up accomplished?  The standard answer 
is that a complete trip to the server is averted, but this is not true, 
in fact a complete cycle does occur:

1)  Request to server
2)  Possible db access on server
3)  rendering of HTML on server
4)  delivery to browser
5)  re-rendering of portions of screen

Supposedly the js and css libraries are cached so we have not saved the 
effort of retrieving them, this means the only thing we have saved is 
the effort of re-rendering the screen from scratch.  To put another way, 
we have not saved a whole lot of bytes of traffic, or CPU cycles on the 
server.  The only thing that seems to be missing is the 
render-from-scratch on the browser. 

Is this correct?  And if so, why is it so dramatically expensive to 
render a page from scratch, that Ajax could make such a dramatic 
improvement to the situation?
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