I have just purchased an Elitebook 8440. It will come with 4GB ram and I have been told the max ram is 8. I have the 4gb ram from the dead laptop. Part number 621569-001. How can I confirm that what I have is good to use in the new computer? I've checked out the HP PartSurfer and the replacement part number is 641369-001 if that helps at all.