Syntax Highlighting Latency in Emacs

[jab3]

Hello -

I don't want to start a war or anything (because it probably has something
to do with my system), but I am curious about something I've noticed with
Emacs as compared with vim.  If I'm looking at a source code file in vim,
(and it doesn't even have to be that large - maybe a few thousand K) the
syntax highlighting is automatic.  And if I edit something, which changes
the highlighting of the rest of the file, it is instantaneous.  But in
Emacs, there is a 2 or 3 second delay in the updating of the highlighting. 
Is there a setting I'm missing somewhere?  (I'm new to Emacs, and I am
trying to move to it instead of vim for serious editing)  Has anyone else
noticed this?

My system is a P4 2Ghz with 256M RAM.


Thanks,
jab3