Kkrust,
The installed memory can be checked a number of different ways, such as in the BIOS/CMOS settings and with third party programs, but an easy way to determine the RAM installed is to RIGHT click on "My Computer", choose "Properties". In the lower right corner of the "General" tab window should be an indication of the RAM installed.
In regards to how much is used, Windows should use all of the memory that is installed so that the computer will operate efficiently. If you want to know how many "resources" are used, which is a strange combination of the number of programs and processes running on the machine, then RIGHT click on "My Computer " choose, "Properties", then click on the "Performance" tab. The amount of "resources" will be listed there. The best baseline for "resources" will be immmediately after start up. Restart the computer, then check them. Resources are at their highest at that point.
Hope this helps.
Grif
How do I check how much memory I have on my computer vs. how much I have used?

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