Activity monitor and system profile aren't matching up in ram amount?

I installed 4GB on my mac, from the 3GB i used to have. I went up to about my mac and I see that both ram slots are detected and it also registers that it has 4GB of ram. When I open activity monitor the pie chart that shows the memory usage says 3.00 GB Is this normal? Why aren't these two numbers matching up?

What model Mac? as in .. Macbook 8,1 etc ?

its a macbook pro intel core 2 duo late 2006 model, in the system profiler it shows up as macbookpro 2,2

it may be that the max supported ram for that mbp is 3GB. Unfortunately, I'm at work, thus don't have MacTracker available. Someone will hopefully pipe up, else.. I'll check when I get home.

Ok, from Mactracker


Maximum Memory 3.0 GB (4.0 GB can be installed, only 3.0 GB will be addressed)
Memory Slots 2 - 200-pin PC2-5300 (667MHz) DDR2 SO-DIMM

Using a matched pair of 4GB will maintain the dual channel capability but will only be able to address 3 GB. Have an '06 myself. It is not physically capable of using all 4 GBs.