A:Under the current PC memory addressing, there is a memory area just below 4.0 GB which is reserved permanently. The maximum DDR memory support is actually about 3.5GB rather than 4GB. This limitation is caused by the current PC architecture in which the missing 0.5GB of memory addresses are reserved for PCI I/O space, AGP aperture mapping space, and other onboard device I/O space. Thus although the chipset datasheet may claim memory support for up to 4GB, the system actually only offers about 3.5GB with four 1GB DDR DIMMs installed. 32 bit processors only support 4GB of address space.