Throughout the history of personal computers, RAM has always been something of a rare commodity, a luxury even. Only a few years ago, ever reaching the memory limit of 4 GB possible under a 32-bit operating system was completely unthinkable. But then, at one time 640 KB were considered enough for anyone. Times change. Right now, DDR2 memory is as cheap as it’s ever been, and equipping your PC with 8 GB will only set you back about €135.

The benefit of having 8 GB of system memory is that the OS has to access the hard drive far less frequently, making Vista feel much snappier. However, several settings in the BIOS and the operating system need to be changed in order for the system to be able to take advantage of that much RAM. Vista 64 still faces a few challenges, not the least of which is often a lack of drivers. At least most standard applications run without issues. On the other hand, none of the current generation of applications can come even remotely close to utilizing the maximum amount of memory installable.

Most users will have a sobering moment after equipping their systems with 4 GB of RAM. Only 3 GB are recognized by the BIOS and by Windows. This is neither a bug nor due to any hardware error. The explanation is simple. 32 bit systems can only address up to 4 GB of memory. Additionally, many add-in cards and on-board controllers require memory addresses in order to be accessible. This is called “Memory Mapped IO” (MMIO). Since this memory range has to lie within the 4 GB, it is subtracted from the installed and available RAM.

Thanks to a technique called memory remapping, it is possible to move around parts of the system memory in such a way that the full 4 GB are still available for use. The trouble is that this feature had to be deactivated in Windows Vista due to compatibility issues.

In order to be able to utilize the entire system memory, you will therefore need to use a 64 bit version of Windows Vista. In this article, we will take a look at memory usage under the 32 and 64 bit versions of Windows Vista and analyze how the operating system behaves with different amounts of RAM.