Video Card RAM as System - Theoretical performance

[expert01]

I was looking at a review on the new Quadro lineup from nVidia, and when I saw the 7000 card with 12GB of GDDR5, it got me thinking: Could you use that as high performance system RAM?

http://www.tomshardware.com/reviews/quadro-5000-firepro-v8800-workstation-graphics,2701-4.html

Doing a quick google search, I found that Linux is able to use graphics RAM as swap space or a RAM drive (although I assume that the proper drivers would let Windows do the same). http://en.gentoo-wiki.com/wiki/Using_Graphics_Card_Memory_as_Swap

I checked Wikipedia, and PC3-17000 RAM appears to have the same bandwidth as a 3.0 PCI_Express x16 slot (although PCI-eX16 has 2.5 times the GT/s?).



So, here lies the real question, if you use the latest GDDR5 as system RAM (or a RAM disk), how would performance compare to system RAM?

 

[Cerb]

I was looking at a review on the new Quadro lineup from nVidia, and when I saw the 7000 card with 12GB of GDDR5, it got me thinking: Could you use that as high performance system RAM?

http://www.tomshardware.com/reviews/quadro-5000-firepro-v8800-workstation-graphics,2701-4.html

Doing a quick google search, I found that Linux is able to use graphics RAM as swap space or a RAM drive (although I assume that the proper drivers would let Windows do the same). http://en.gentoo-wiki.com/wiki/Using_Graphics_Card_Memory_as_Swap

I checked Wikipedia, and PC3-17000 RAM appears to have the same bandwidth as a 3.0 PCI_Express x16 slot (although PCI-eX16 has 2.5 times the GT/s?).



So, here lies the real question, if you use the latest GDDR5 as system RAM (or a RAM disk), how would performance compare to system RAM?

As RAM: very poor. Right now, we have plenty of RAM bandwidth for desktops. Servers and workstations can stretch it, but 3x1333 is still more than they need, right now (with 1600 being cheap enough, 2000 not being expensive, and 2400MHz+ DDR4 right around the corner).

Latency, which is better on faster DDR3 than it was on faster DDR2, which was better than faster DDR, and so on, is much more important, once a certain level of bandwidth has been reached. We'll keep going up in bandwidth, but lately, we've been increasing it faster than CPUs have needed it (given that IGP has been improving a great deal, typical users are reaping the benefits as much as power users swapping it out with the video card).

Going out to the video card is just going to be too long of a trip, GDDR is tweaked for higher speeds at the cost of latencies, and the video card's memory controller will not be good with kind of small, often unpredictable reads and writes CPUs like to make.

However, as swap, or a RAM drive, it should be insane. The only real issue there is that if you can afford such a Quadro, 16GB+ of main system RAM will be a cheap addition to your machine.