How to add more usable RAM for Win 7 Professional 32bits system ?

I am using a Windows 7 Professional OS, just got my 4GB RAM today. But after I installed it into my computer,the maximum usable RAM still remained at 1.99GB. Isn't Windows 7 Professional can use Maximum 4GB RAM ? How should I adjust my system setting to increase the maximum usable RAM ?

The RAM display in the System property now is  RAM:  6GB (1.99GB usable).

PS. I am not sure if this is relevant, but in my system setting, the Virtue memory is set to be 2GB, I have 6GB RAM, so I don't think it's causing this problem ...

If you have 6GB of RAM, it's waste. You shouldn't have more than 4GB.

All 32-bit client versions of Windows (not just XP/Vista/7/8) have a  4GB address space (64-bit versions can use much more). That's the theoretical upper limit beyond which you can not go.

But you can't use the entire  address space. Even though you have a  4GB address space, you can only use *around* 3.1GB of RAM. That's because some of that space is used by hardware and is not available to the operating system and applications. The amount you can use varies, depending on what hardware you have installed, but can range from as little as 2GB to as much as 3.5GB. It's usually around 3.1GB.

Note that the hardware is using the address *space*, not the actual RAM itself. If you have a greater amount of RAM, the rest of the RAM goes unused because there is no address space to map it to.

4GB is the maximum for any 32 bit OS. I would suggest that you install only the 4GB that you purchased (removing the original 2GB). Consult your manual for optimum slot placement. If in doubt, the slots where the original 2GB were placed would be the best bet (assuming it is 2 x 1GB sticks).

Even then you may find that not all of your 4GB memory is available. Some might be allocated to hardware resources such as your graphics card. There are many articles on this forum explaining this (and elsewhere on the internet).

Tricky