“I just upgraded my desktop computer from 2 GB of memory to 4 GB with the hope that I’ll be able to use it for another year or two before I finally have to break down and upgrade it. However, I was greeted with a most unpleasant surprise when I restarted my computer. When I right-clicked “Computer” and went to “Properties” to view my system information, Windows reported that I only had about 3.5 GB of memory installed. Why can Windows only see some of the memory that I installed? Could one of the memory modules be bad?”
I can say with almost complete certainty that there is nothing wrong with your computer or the memory that you installed. Most likely, you are running a 32-bit version of Windows and have come up against what is known as the “4 GB barrier.” Some websites, such as Wikipedia, actually refer to it as the “3 GB barrier” for whatever reason. What it comes down to is that, when running a 32-bit operating system, you have a maximum of 2^32 or 4,294,967,296 possible memory locations that the computer can address, which translates to 4,096 MB. This limit applies to all of the memory in your computer. So, for example, if you have a video card with 1 GB of memory, it’s going to consume 1 GB of the available memory locations and leave your operating system with 3 GB of available RAM.
Some 32-bit operating systems get around this problem using a feature called Physical Address Extension (PAE) to overcome this limit and allow the computer to utilize all of its installed memory. Some of the operating systems supporting this feature are Windows 2000 Advanced Server and Windows Server 2003 Enterprise Edition. However, using PAE you can run into certain problems. Some motherboards may not have proper support for PAE, and when the operating system accesses memory above the 4 GB barrier, the computer takes a performance hit.
Since installing an expensive server operating system probably isn’t what you had in mind, your two best options are to either put up with the limit and understand that your computer won’t be able to use the full amount of installed memory or to install a 64-bit version of Windows. For example, the 64-bit version of Windows 7 Home Premium supports up to 16 GB of memory, while the Professional, Enterprise and Ultimate editions support up to 192 GB.
Can you install a 64-bit operating system? If your computer isn’t more than a few years old, it’s likely that the answer is “yes.” Some of the Intel processors that support 64-bit Windows include the Core i series, the Core 2 series, the Pentium Extreme Edition series and many processors from the Pentium Dual-Core, Atom and Xeon product lines. Because Intel rival AMD developed the 64-bit implementation that Intel now uses for most of its processors, AMD has been supporting 64-bit operating systems for years. Some of the AMD processors that support 64-bit Windows include the Athlon 64, the Athlon II, the Athlon X2, the Opteron, the Turion and the Phenom.
Because 64-bit versions of Windows have no trouble running 32-bit software, you can install one without fear that you will lose the ability to install your current software. Assuming that you’re going to install 64-bit Windows 7 or Windows 8, the experience will be almost exactly the same as it was with a 32-bit operating system. In fact, within the next year or two, all home computers are likely to be 64-bit, so you have nothing to lose if you make the transition now.
