understanding CPU stats

[alex at crackpot.org]

I'm trying to better understand the output of vmstat, specifically the  
difference between 'user' and 'system' cpu usage.  I have guessed that  
'user' is all user programs, and 'system' is the kernel.  Is that right?

I've just upgraded PHP versions, and I'm seeing much higher system cpu  
usage than prior to the upgrade.  Not sure what to attribute that to,  
or where I ought to look for optimization options.

Memory usage looks about the same before and after.

alex