Recently I decided to make one old school rig with spare parts I have ( all of them working). So I used my old Asus A8N - SLI motherboard with 2 Asus GF8600GT (Silent EN8600GT) 512VRAM each and 3 GB DDR400 A-data (2x1GB +2x512 MB - all with same clocks and from same series) and Athlon 64 X2 Dual Core 3800+ @ 2.00 GHz. Everything works great, Win7 x64 Ultimate installed. The issue is that in BIOS there is listed that I have installed 3072 MB RAM, but usable 2560 MB RAM. Because of that Windows ofcourse shows 3GB (usable 2.5GB - the other 512MB is hardware reserved). I searched through google and some forums, and someone mentioned that this is normal because the SLI I used. Because thats my first time I use SLI, want to ask is that normal and can someone explain me if its normal, why it is normal ?
P.S. In my BIOS the options about S/W and H/W over 4GB remapping are enabled, the memory is set to 400Mhz with correct timings according CPU-Z and Everest Ultimate 5.50.
If you installed total 4GB memory, the system will detect less than 4GB of total memory because of address space allocation for other critical functions, such as:
- System BIOS (including motherboard, add-on cards, etc..)
- Motherboards resources
- Memory mapped I/O
- configuration for AGP/PCI-Ex/PCI
- Other memory allocations for PCI devices
Different onboard devices and different add-on cards (devices) will result of different total memory size.
e.g. more PCI cards installed will require more memory resources, resulting of less memory free for other uses.
On a SLI system, since PCI-Ex graphic cards will occupy around 256MB, another 256MB will be occupied after you install a 2nd PCI-Ex graphic card. Hence, 2.75GB memory left only if two SLI cards installed on A8N-SLI Premium while 3.0GB memory left with one graphic card without other add-on devices.
This limitation applies to most chipsets & Microsoft Windows 32-bit version operating systems.
So if I get it right - in my case I have 3GB physical memory installed, the BIOS detect them, but reserves 2x256 MB RAM (256mb for each card i have installed) and leave me 2.5GB RAM to use ? If I install 4GB RAM, will there be detected 4GB RAM and 3.5GB usable or the amount of RAM reserved is scalable with the amount RAM installed ?
Ok, I think I get it. The only way to discover how much exactly RAM will be reserved if set 4x1GB RAM is to buy 2x1GB new ones to replace the 2x512MB I have at the moment. Thanks a lot for the info and the answer!