By default, the drivers and the Windows kernel is loaded into virtual memory (swap file), in layman's terms they are loaded on a virtual space on the hard disk. If you have enough RAM is available, it is possible to force load kernel and drivers in RAM (memory), which can significantly improve system performance. However, if the amount of RAM available is not large enough, this can block your system
The recommended values of RAM for XP and 2000 are respectively 128 and 256 MB or twice if intensive applications are used. Under Windows 7, it is recommended to have at least 4GB of RAM.