Three things I've always wondered when it comes to system RAM and a GPUs VRAM

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opio

opio

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1. Let's say my GPU only has 2GB of VRAM but the game or video editing app I'm using needs more. What happens then? Does the GPU access and borrow space on system RAM? I guess a better question is: Can your GPU even access system RAM?

2. Another question I have is this: Why do GPU's seem to be ahead when it comes to volatile memory? System RAM just went to DDR4 but GDDR5 GPUs have been out for like 3 or 4 years. Can't they just adapt GPU VRAM technology to make system memory faster? Or at least on par with video memory?

3. Assuming that your GPU could access system RAM if it needed to, would DDR4 create a bottleneck?


Dammit, I just wish that when you sli/xfire the VRAM stacked instead of remaining the same.
e.g. Two GPUs in sli with 2GB VRAM still has just 2GB VRAM instead of 4GB.

 
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Tradesman1
DRAM used in video cards (GDDR5) is simply another iteration of DDR, and is faster. Yes some GPUs that don't have enough RAM can effectively share system DRAM (not as efficient as having on-board DRAM on the discrete card. Also, iGPU use system DRAM and they too benefit from faster system DRAM - if using an iGPU you also want to account for it in your specs for the rig because it's not available for base system use.

As to the above statement that was offered "you could use faster RAM as system RAM but the CPU could not keep up with it." it doesn't even make sense ;) Sorry but the DRAM doesn't tell anything what to do so the CPU has no need to keep up with it. Not to mention common sense. CPUs have long run with DRAM faster...
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weberdarren97

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1. When a GPU runs out of VRAM, it will use system memory. However, the system can never use a GPU's VRAM as system memory.

2. The amount of research and engineering required to create a new type of graphics memory is huge. If you want to adapt that memory to be put in as system memory, that also takes a lot of research and engineering. Simply put, it takes time to create a new type of memory.

3. The DDR4 itself wouldn't create a bottleneck, but the PCIe slot would. It wouldn't be able to access the system memory as quickly as it can access its own VRAM because of all the chatter that's already going on through the PCIe slot. It would be slow, yes, but the DDR4 itself wouldn't be the bottleneck.

4. This is because of the nature of SLI/Crossfire. Instead of the two GPUs working together on a frame, they each work on separate frames at the same time. This means that the load on each card is essentially half, but you don't get 2x performance because of hardware overhead. You actually get closer to 1.5x the performance of a single card.
 
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Samer1970

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MERGED QUESTION
Question from opio : "3 things I have always wondered about system RAM and GPU VRAM"



some VGA cards can use System RAM , but not the Gaming cards .. Gaming cards dont do this.
 
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JackNaylorPE

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People have been ranting about VRAM for years... just about always based upon misinformation.

1. When the 7xx series from nVidia was current, peeps were clamoring for 4GB, testing (alienbabeltech) showed that no game ever actually used or performed better with 4 GB than 2 GB (5760 x 1080)

2. When 9xx series was current, the clamor was for more than 4 GB and yet no game ever used more than 4Gb at resolutions uo to 1440p
http://www.extremetech.com/gaming/213069-is-4gb-of-vram-enough-amds-fury-x-faces-off-with-nvidias-gtx-980-ti-titan-x

The reason for peeps misconception was that they use GPUz and **it says** something but not what they think it says. When you launch a game, it **allocates** a certain amount of RAM.... kinda like a credit card company might allocate you a $5,000 spending limit. So if you spend $1,000 on that CC, and then you go for a car loan, what amount "goes against" you ability to pay back the loan ... mo it ios not $1,000, it's $5,000.

Same thing... GPUz reports what has been allocated for the game to use. not what it actually uses. If you have 2 GB at 1080p * you are JUST FINE ... if you have 4 GB at 1440p *, you are JUST FINE.

* outside perhaps of very poor console ports.

http://alienbabeltech.com/main/gtx-770-4gb-vs-2gb-tested/3/
http://www.guru3d.com/articles_pages/gigabyte_geforce_gtx_960_g1_gaming_4gb_review,12.html
https://www.pugetsystems.com/labs/articles/Video-Card-Performance-2GB-vs-4GB-Memory-154/
http://www.extremetech.com/gaming/213069-is-4gb-of-vram-enough-amds-fury-x-faces-off-with-nvidias-gtx-980-ti-titan-x


3. System RAM and VRAM are different

4. GPUs benefit from faster RAM, you coulkd use faster RAM as system RAM but the CPU could not keep up with it.
 
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opio

opio

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Wait so GPUs meant for gaming can't access system RAM? I have one guy here who says it can and another who says it can't

P.S. I know why sli/xfire VRAM doesn't stack and all about alternate frame rendering and whatnot, I just meant I wished it stacked haha, Which I guess it could if one card rendered half of the screen while the other card rendered the other half, but my guess is that this would result in some serious tearing.
 
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Tradesman1

Tradesman1

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DRAM used in video cards (GDDR5) is simply another iteration of DDR, and is faster. Yes some GPUs that don't have enough RAM can effectively share system DRAM (not as efficient as having on-board DRAM on the discrete card. Also, iGPU use system DRAM and they too benefit from faster system DRAM - if using an iGPU you also want to account for it in your specs for the rig because it's not available for base system use.

As to the above statement that was offered "you could use faster RAM as system RAM but the CPU could not keep up with it." it doesn't even make sense ;) Sorry but the DRAM doesn't tell anything what to do so the CPU has no need to keep up with it. Not to mention common sense. CPUs have long run with DRAM faster than they are made to use, however they do have to run with DRAM of the architecture they were designed to run with. If say a Skylake (which can run DDR3 or DDR4) had been designed to run with DDR5 specs in mind, then it could. ;)
 
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