...In theory,
a 32-bit operating system should be able to support 2[SUP]32[/SUP] bytes = 4GB memory. Thus the first reaction usually is that the memory chips or with the mainboard has a hardware defect. Unfortunately, that’s not the case. Vista can indeed address 4GB of memory. However, the maximum amount of RAM that can be used by the system and applications is 3.12 GB.
The cause for this is the so-called
memory-mapped I/O (MMIO). Some devices need a dedicated space in memory. A typical example is a video card that utilizes the system memory. Now, you might object that your video card has its own memory and you didn’t install any additional devices that could occupy so much RAM.
Well, for compatibility reasons Vista
reserves memory for devices even if they don’t exist in your computer. ...
...
The only problem is that those who are unaware of Vista’s 3.12 GB limit just wasted their money. If you really want to know how much memory Vista actually uses, you have to use
Vista’s System Information tool. To do so, go to Vista’s Start prompt and type
Msinfo32. The new System Information tool in Vista SP1 distinguishes between “Installed Physical Memory (RAM)” and “Total Physical Memory”. The latter one is the amount of memory you can really use, and the first one indicates how much money you just have wasted if you put 4GB in your PC. You can read more about this issue in
this KB article.
