Ram

I currently have a P4 with over 300 MB of ram. 2 are DDR256 MB and one sdram 64 MB. My machine seems pretty slow for all of that state of the art hardware. A guy in work told me that your computer will only run as fast as your lowest ram chip which is 64MB. Is this true?
Thank you very much in advance.
dennis.e.whitehead@questdiagnostics.com