The main reason to switch to a 64-bit operating system is to use a greater amount of RAM in your PC. Because 32-bit operating systems can only address a maximum of 4GB of RAM, any amount of memory that exceeds the 4GB limit, will be rendered useless.
While 32-bit operating systems can theoretically address 4GB of RAM, Windows operating systems such as Vista and 7 can realistically only address 3 to 3.3GB of RAM.
So if you install 4GB of RAM (a very popular choice today) in your computer while running a 32-bit Windows operating system, your computer will only use 3.3GB of RAM, leaving the rest to waste.
The good news is that Windows can “see” and use the entire amount of 4GB if you have a 64-bit compatible CPU.
How do you know that you have a 64-bit compatible CPU?
Well if you’ve bought your computer in the last 2 years you most likely have a 64-bit compatible CPU. Of course, it doesn’t hurt to check and make sure.
Point your browser to: http://www.cpuid.com/cpuz.php and download CPU-Z, a free utility that gives you detailed information about your CPU and other important PC components.
On the top left side of the window, under the Download Latest version section, click the CPU-Z 1.54 setup (english) link and save the setup file on your Desktop (or your preferred download folder).
Double-click the cpuz_154_setup.exe file and click Next in the setup dialog window.
Check the I accept the agreement option and click Next again. Continue to click Next two more times to install CPU-Z in your default installation folder.
At the next step uncheck all the checkboxes if you don’t want to install Ask.com’s toolbar and proceed with the final Next.
Click Install to begin the installation process and Finish to end the setup dialog window.
You should now see a CPU-Z shortcut on your Desktop. Double-click on it to launch the application.
On the first tab (CPU), look in the Instructions field (in the middle of the window).
If you have an Intel CPU check to see if you have the EM64T instruction, for an AMD CPU check to see if you have the x86-x64 instruction.
This means you have a 64-bit compatible CPU and can use the full 4 GB of RAM installed in your system.
If you don’t see these instructions then you do not have a 64-bit compatible CPU and you will have to switch to a 64-bit operating system to benefit from the full 4 GB of RAM installed in your system.
After checking your CPU compatibility, you can close the CPU-Z application by clicking the red X button or even uninstall it from your computer since we won’t use it anymore.
OK, we’ve established that you have a 64-bit compatible CPU, now it’s time to bring up the command prompt and force Windows to use all your installed RAM (up to 4GB).
We can achieve this by enabling a processor feature named PAE (Physical Address Extension).
PAE enables several advanced system and processor features allowing 32-bit Windows operating systems to address 4GB of RAM.
Note: PAE is supported by the following 32-bit Windows operating systems: Vista, 7. This tutorial is based on the Vista operating system. The following steps may be slightly different on other Windows operating systems. Also, note that if you have a 64-bit operating system, it can use up to 192 GB of RAM (Windows 7 Ultimate) and there is no point in using this article.
Now, to open a command prompt, go to the Start menu and type cmd in the search field. Then, right-click on the cmd icon and select Run as administrator.
With the command prompt open, type in the following command and press Enter from the keyboard:
bcdedit /set pae forceenable
You should see the message: The operation completed successfully. If you see an error message, check your spelling and make sure you typed in the command exactly.
Now close the command prompt and restart your computer.
After the restart, go to the Start menu, right-click the Computer option and select Properties.
In the basic information window, look in the Memory (RAM) field and you should see 4GB of RAM (if you have 4 GB installed in your computer).
Note: PAE may cause your computer to run slower because it has to use an extra addressing cycle.
If you want to turn off PAE because your computer is running to slow or the above command did not work, repeat the above steps to open a console prompt, type in the following commands and press Enter from your keyboard after each one. After that, restart your computer:
bcdedit /set nx alwaysoff
bcdedit /set pae forcedisable
Note: When you disable PAE, you also disable DEP (Data Execution Prevention). DEP allows Windows to prevent malicious software from accessing your computer’s memory. If your computer’s hardware does not support DEP, turning it off will not change anything.