RAM Question

Hi Forgive me for a beginners question!! I have 4GB of RAM installed on my computer with Vista Home Premium 64bit. When I look at the system information It says that I have 4GB Installed Physical Memory, 4GB Total Physical Memory but only 2.55GB Available Physical Memory. Does this mean that the other 1.45Gb is being used somewhere else or can I increase 'Available Physical Memory'? I basically want to make the most of my 4GB of RAM. Thanks for any help

this isn't exactly an answer to your question, but remember that some of the ram is going to be used just because the computer is running--and a lot more because of the x64 architecture. the photo is of my home premium x64 system. but i want to add also, that i have a laptop that has the 32-bit home premium installed and when i look at the task manager, i have only about 970-990 MB of memory being used on the laptop. you can see from the photo--with only my web browser open (on my x64 system) that i almost have 2 full gigs of memory being used.

Thanks for the reply mpcrsc562. I see now that the available RAM changes. I thought number was staying the same