System Memory RAM <= GPU Video VRAM

[nenforcer]

With the prevalence of GPU's with framebuffers larger than 1GB now, up to 2, 3 or even 4GB, there are bound to be people with older systems (possibly still XP) who are purchasing even low end graphics cards with 2GB GDDR3 graphics memory when they only have maybe 2GB of system RAM or less.

Does anyone know if it is OK for an OS which handles a GPU with 2GB of VRAM with only 1GB of system RAM (like the PC in my sig) or does their need to be as a minimum at least as much system memory (and preferably more) as there is for a GPU?

I haven't heard of someone running a 2GB GPU in a PC with only 1 GB of system memory and I know in XP even though it is 32-bit it can only really handle about 3GB of system memory.

Since RAM is so cheap nowadays and most new PC's come with at the very minimum 8GB maybe this just isn't an issue. I for the life of me can't find any system requirements for GPU's which state that you need >= more system memory than the GPU has to correctly address all of it. I'm guessing the OS can somehow accomodate these large GPU's VRAM buffers.

 

[Jaydip]

Windows 32 bit can't address more than 3Gb ram regardless of how much vram do you have.

 

[nenforcer]

Windows 32 bit can't address more than 3Gb ram regardless of how much vram do you have.

So you couldn't run Windows XP with 2GB system memory along with a 2GB VRAM video card? Is that a physical limitation of Windows XP?

 

[Jaydip]

It is limitation of a 32bit architecture.For eg if you have 4Gb ram on a 32bit machine You can't use them all

 

[ShintaiDK]

So you couldn't run Windows XP with 2GB system memory along with a 2GB VRAM video card? Is that a physical limitation of Windows XP?

I assume you think on mapped memory space. And thats wrong. Its a simple BIOS matter and not related to the OS. You can run a 4GB GFX card on a 32bit OS with 3GB for example and utilize it all fully.

32bit OSes can use up to 64GB with PAE.

 

[Jaydip]

I assume you think on mapped memory space. And thats wrong. Its a simple BIOS matter and not related to the OS. You can run a 4GB GFX card on a 32bit OS with 3GB for example and utilize it all fully.

32bit OSes can use up to 64GB with PAE.

Its actually a boot.ini matter(add the /pae switch) :biggrin:
But not all 32bit os can use 64gb,it depends on the os

 

[nenforcer]

Apparently there is another switch you can use on Windows Vista 32-bit and Windows 7 32-bit which alters the amount of system RAM available to a user process

bcdedit /set IncreaseUserVA 3072

which increases the amount of system memory available to user processes vs. system processes. I guess the default is 2GB to 2GB and the command above allocates 3GB of system memory to user processes while leaving the remaining 1GB to system processes.

It doesn't say anything in regards to if this is accessible to the GPU VRAM but there are numerous thread on games like Witcher 2 and applications like Adobe CS2 and people swear by it.

 

[lamedude]

Only 512MB IIRC of the GPU's VRAM gets mapped so you can have a 4GB GPU on XP. But in D3D9 most assets like textures in video memory are duplicated in system memory. D3D10/WDDM fixes this.

 

[ShintaiDK]

Apparently there is another switch you can use on Windows Vista 32-bit and Windows 7 32-bit which alters the amount of system RAM available to a user process

bcdedit /set IncreaseUserVA 3072

which increases the amount of system memory available to user processes vs. system processes. I guess the default is 2GB to 2GB and the command above allocates 3GB of system memory to user processes while leaving the remaining 1GB to system processes.

It doesn't say anything in regards to if this is accessible to the GPU VRAM but there are numerous thread on games like Witcher 2 and applications like Adobe CS2 and people swear by it.

Same as /3GB switch in NT4/2000/XP.

 

[Magic Carpet]

Does anyone know if it is OK for an OS which handles a GPU with 2GB of VRAM with only 1GB of system RAM (like the PC in my sig) or does their need to be as a minimum at least as much system memory (and preferably more) as there is for a GPU?

There are no strict guidelines. You can use a card with 4 gigs of video memory if you want. Modern games do require at least 2 gigs of system ram for decent gaming, however. If you are system ram limited, a fast SSD could help in this case.

So you couldn't run Windows XP with 2GB system memory along with a 2GB VRAM video card? Is that a physical limitation of Windows XP?

I gamed yesterday on such a system, in fact. Crysis 2 ran flawlessly @ 1050p (max GPU memory usage was 1193 MB, total system memory peaked @ 1722 MB).

 

[ViRGE]

Only 512MB IIRC of the GPU's VRAM gets mapped so you can have a 4GB GPU on XP.

This is the single best answer in this thread. GPU VRAM stopped being directly mapped on 32bit OSes ages ago when it became apparent direct mapping would be an issue. I'm not sure if 512MB is the right value, but you're definitely not mapping all of a 2GB/3GB card's RAM to virtual memory on 32bit Windows.

 

[Cerb]

32bit OSes can use up to 64GB with PAE.

A bit OT, but that is only conditionally true. MS allows it on servers, but all currently-supported desktop OSes are capped to 4GB, unless 8 is an exception, due partly to not requiring that drivers function correctly with high addresses in PAE mode, including MS' own drivers and parts of the HAL, from what I've read (also that by the time it really mattered for non-servers, x86_64 was around, so they wanted people to move to 64-bit Vista).