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Asus A8N-SLI Memory issue using SLI

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  • Asus
  • SLI
  • Motherboards
  • Memory
Last response: in Motherboards
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May 11, 2014 5:20:11 AM

Hello

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.

Best regards!

More about : asus a8n sli memory issue sli

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a b } Memory
May 11, 2014 11:00:37 AM

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.
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May 11, 2014 1:23:27 PM

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 ?
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a b Ĉ ASUS
a c 338 V Motherboard
a b } Memory
May 11, 2014 2:30:46 PM

Also, you'll have additional memory 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 PCI
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May 11, 2014 10:33:44 PM

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!

Best regards!
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