Eugenio,
Please check the following information available on the TPS of your motherboard. http://www.intel.com/support/motherboards/desktop/d945gnt/sb/CS-029359.htm
“The board utilizes 4 GB of addressable system memory. Typically the address space that is allocated for PCI Conventional bus add-in cards, PCI Express configuration space, BIOS (SPI Flash), and chipset overhead resides above the top of DRAM (total system memory). On a system that has 4 GB of system memory installed, it is not possible to use all of the installed memory due to system address space being allocated for other system critical functions. These functions include the following:
- BIOS/ SPI Flash (2 MB)
- Local APIC (19 MB)
- Digital Media Interface (40 MB)
- Front side bus interrupts (17 MB)
- PCI Express configuration space (256 MB)
- MCH base address registers, internal graphics ranges, PCI Express ports (up to 512 MB)
- Memory-mapped I/O that is dynamically allocated for PCI Conventional and PCI Express add-in Cards “
So, this is the math, if we add all the MB from the list, it is equals to 846 MB.
1GB =1024MB
4GB = 4096MB
4096MB-846MB =3250 MB
3.25 GB total to be use.
This board is not capable to map more than 4 GB of memory, therefore when you are using only 2GB, the board does not need to reserve the amount of memory (846MB). That is for design.
Hope this information help you.
Regards.