Check your owner's manual (which may be a PDF on the had drive) or search
the HP support website for a manual/info on the ammount and kind of RAM the
PC supports.
Be aware that some RAM must be installed in pairs, others can be installed
as single units. Further, sometimes there are limiations on using all RAM
slots, or on the order they must be used. Finally, all PC's have some upper
limit on the supported RAM, is often less than the maximum supported by the
operating system.