Allocate unused RAM for 780g video memory

[zackcentury]

Hi, I'm new to Tom's and computer building, but I'm going to be building a new system soon anyway. I'm using an AMD 5200+, 4gb ram, and a Gigabyte 780g mobo, either GA-MA78g ds3hp or one of the sh2 models, and running Vista 32bit. I understand Vista can only make use of about 3.5gb of ram. And according to this article, http://www.tomshardware.com/reviews/amd-780g-chipset,1785-2.html

The motherboard's BIOS lets you borrow 128, 256 or 512 MB of RAM from the system's RAM, to allocate it as video memory to the integrated GPU. For the first time ever, AMD is also equipping its integrated graphics chip with a separate memory interface. This allows motherboard makers and OEMs to provide dedicated graphics memory for the integrated chip directly on the board, if they find the GPU's performance unsatisfactory, or don't wish to use a shared-memory solution. In effect, this transforms the integrated on-chip graphics solution into a dedicated graphics card that just happens to reside in the northbridge.

the BIOS in Gigabyte boards allows you to allocate 128, 256, or 512mb of system memory for the on board video. Two questions:

Will this memory be shared with the 3.5 or so that Vista uses, or is it possible that the memory will be the unused portion of the 4gb?

And does anyone know if this feature is common in all Gigabyte 780g boards?

thanks

 

[Scotteq]

Memory mapped I/O, is memory mapped I/O, is memory Mapped I/O.


The limitation isn't Vista's, it is inherent in all 32 bit Operating systems. There is only a total of 4GB "worth" of addresses to use for system resources to use, so the short answer is "Ultimately it all comes out of the same bucket. So when you run out, that's it." Now, Gigabyte may have a way to allocate it a little more efficiently. But for details on that, I'd recommend going to the source rather than depending on a message board for accurate detailia on a manufacturer specific feature.

On the server side, there are a couple tricks to get around it, but on the consumer side you're basically stuck since MSFT don't allow PAE extensions on consumer versions of their OS's.

Or...

You can use a 64 bit version of the OS, and bypass the issue altogether.

 

[zackcentury]

Memory mapped I/O, is memory mapped I/O, is memory Mapped I/O.
Now, Gigabyte may have a way to allocate it a little more efficiently. But for details on that, I'd recommend going to the source rather than depending on a message board for accurate detailia on a manufacturer specific feature.

Yeah I suppose I will ask gigabyte since neither this nor other forums have been able to answer. I just imagined that with ram so cheap and the 780g boards being popular and affordable, someone would have had the same idea and tried to figure it out. I guess with so much ram though, it might not make much difference to me anyway.

 

[notherdude]

First let's get one thing straight. Vista or XP rerely end up with 3.5 available. The OP mentions 3.5 but 3.5 is the high end of available RAM and we rarely ever see this anymore because of video cards coming with so much RAM. You used to see 3.5 when you had video cards with 64 meg Vram or so. Now you typically see about 3.2 or even less, sometimes much less. The system allocates memory space for the video card RAM and for the other devices with ram on them. So it isn't simply a matter of subtracting video ram.

I'm thinking the amount you allocate to video ram will simply come off the 4 gig as it usually does (though it is not always a simple subtraction) and not off the 3 or 3.5. In other words let's say you start with 4 gig of system ram and no memory mapped i\o, you would have 4 gig of memory space available, now you add in memory mapped i/o including say the extra 512 of system ram you choose to allocate to video on this special mobo. You would likely end up with about 3.5 minus the extra reserved for other, non-video i/o, so you end up with about 3 to 3.2 which is what we usually see on a system with a 512 video card. (

In other words this system should end up with the same amount of available RAM as a system with the same amount of dedicated memory on the video card. Otherwise you would lose 2x the amount you allocate to the gpu.

To sum up I think you will have about 3 to 3.2 gig available ram if you choose to allocate 512 to the video card - the same as normal systems with a video card with 512 on the card.

 

[zackcentury]

Oh thanks notherdude. It would be great if it worked out that way, I'll either contact gigabyte or just play around with my system when I finally get it together. I was just trying to decide on the mobo and memory configuration for my final purchases. And the 3.5 was just an estimate, I have not actually used a system like this before.