Mechanics of Video Ram?

Can anyone explain the technical side of Video Ram? Latency and speed are obvious, but what I'm interested in is whats the difference in performance between the same card with 256mb vs 512mb vs 1024mb...

I have a 7900gt with 256mb ram, I get the distinct feeling that WoW is loading more than 256mb of textures straight away, and this is where I'm feeling a bottleneck on my system, I can run 2 copies with no performance hit, which would make sense if this is the case since both would be utilizing system ram for the overflow of textures... (I believe that AGP and PCI-Express both utilize system memory if they run out of on board memory...)

Now I'm no expert (quite far from it, even), but from what I've picked up, video card memory is basicly how much your screen can hold at one given timestamp. The more memory, the greater the resolution you can set (given that the bus speed, and the likes of it, 're high enough).

By all means, feel free to correct me, as I was given a 30 second explenation narrowed down from a 30 min presentation xP

That was my understanding as well back in the world of Voodoo2's and the like.

Most of the video cards of that era had 4mb video ram and 12mb of texture memory. As resolutions increased and textures got bigger and more detailed we saw spikes in those, but at some point I get the distinct feeling that texture/video ram merged into a single body and I am sure one of the distinct advantages (disadvantages?) of AGP and PCI-Express was that they could tap system resources if they ran low of onboard, this would of course cause swapping, bus saturation, and other performance hits, but you wouldn't see black/gray dropped textures or system crashes due to memory issues.

However, I stopped being a hardware guy nearly 8 years ago, I do research on what performs well each time I buy a new system, every 2-3 years, but this last round has left me disappointed in the overall performance of the system despite having relatively high end hardware. I'm trying to find the bottleneck and short of dropping another $350-400 on a 512mb card I'd like to KNOW that the extra video ram would help... running a single instance of WoW my friends PC (nearly identical to mine except a 6400+ instead of a 6000+ and a 8800gtx instead of a 7900gt only see's a 10fps gain in Shatrah... meanwhile friends running intel boxes with 512mb-768mb of video ram are seeing 100+FPS in shatrah...

Basically I'm looking for the answer to this question...
Do I buy a new mainboard, quad core intel chip, and ram, or do I upgrade my 7900gt... which despite being a year old is STILL a damn fine video card with 256mb of ram.

Quote:

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Originally Posted by zanthor

Basically I'm looking for the answer to this question...
Do I buy a new mainboard, quad core intel chip, and ram, or do I upgrade my 7900gt... which despite being a year old is STILL a damn fine video card with 256mb of ram.

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The original question you asked is far outside the scope of this forum. Google up "GPU architecture" and start reading some of that and it might shed some light on things. With the advent of the GPU, the VRAM is used for a lot more these days than it used to be.

As for this more specific question, I would most definitely upgrade your mobo/CPU/RAM first as that card is indeed a fine performer for what WoW does. Now, if you want to be able to drool over Crysis or other bleeding-edge games, the answer is "it depends." :P

The amount of RAM on the video card has almost nothing to do with performance. All other factors being equal, less RAM will only cause a slight amount of slowness if the game is using very detailed textures (like Crysis or other newer games). 256MB or video ram should be more than enough for a single instance of WoW. If you run more than one instance of WoW though, then you may want more video RAM. However, if you are going to spend money on a new card, don't worry about the amount of RAM on it. Just pay attention to real world benchmarks on places like Tom's Hardware. Many companies use marketing hype and put more RAM on slower cards to lure people into thinking they are better.

As far as your question about what to upgrade, Intel's Core 2 procs are a decent bit faster than AMD's current line, although AMD's tend to be cheaper. I upgraded from an AMD Athlon X2 3800+ to an Intel Core 2 Quad and it made a HUGE difference (had an 8800GTX and 2GB RAM in both situations)

Edit - found this on the Burning Crusade system requirements page:
PC System Requirements

* OS: Windows 2000 (Service Pack 4) or Windows XP (Service Pack 2)
* Processor: Intel Pentium3 800MHz or AMD Athlon 800MHz
* Memory:
o Minimum: 512 MB RAM
o Recommended: 1GB RAM
* Video:
o Minimum: 32MB 3D graphics processor with Hardware Transform and Lighting, such as an NVIDIA GeForce 2 class card or above
o Recommended: 64MB VRAM 3D graphics processor with Vertex and Pixel Shader capability, such as an NVIDIA GeForce FX 5700 class card or above
* Sound: DirectX-compatible sound card

So just multiply the recommended numbers for each instance of WoW you are running and that should approximate what you need. =)

BTW, the 7900gt is a (nearly) 2 year old architecture. I've had my 8800GTX for a year now. The 7900 series came out about 6 months before the 8800gtx, but it is still based on the 7xxx series architecture.

Without researching it I would venture an educated guess is that more video ram allows you to store more umm texture palets or whatever parts of the world are called, the stuff that is loaded when you zone.

Thus if you are just doing one instance additional video ram is not needed. If you are running 4 instances then you would want more video ram.

7900 is gathering dust on my self, having replaced it with a 7950, then replacing that with a 6600 and replaceing that with 8600 ... lol

video ram is used to improve performance when rendering scenes while also helping with double/triple buffering to provide smooth animation with no flicker.

basically, the biggest impact is moving data from system memory across the system bus to graphics memory. if the screen is rendered in system memory, like some laptops do when they use 'shared' memory, then the screen, or portions of it, gets shipped across the bus 60+ times per second.

instead, you ship the components you'll need to work with over to graphics memory... then render the scene over there... at which point, pushing it to the screen is fast.

having more memory allows you to store more components. for multi boxers trying to run 4+ wows per machine, this is critical... as each application 'locks' its sections.

so, if you are running 4 wows...and have 64M of memory, you really only have 16M each. 256M would mean each wow would have about 64M.. and 512M would yield 128M each.

it's been a while since i've done directX, but that's the gist of it.

Ok, so a logical jump here would be that peoples framerates drop in Shattrah not necessarily due to number of polygons but rather the number of textures required since you are flooded with player models which are all unique in some fashion or another... which could explain why my 256mb 7900 doesn't show me the performance I'd expect yet can still run 2 copies of wow as it's having to move textures in and out of video ram as they are needed?

Or am I way off base here...

As to the advice to upgraid mainboard, cpu and ram, there isn't a lot of "up" I can go from an x2 6000, yes, there are higher end intel chips out there, but all said and done I'd be looking at a moderate gain since the CPU doesn't seem to be the chokepoint at all. I already intend to bump up to 4gb of ram, however before I drop that cash I'll be stealing the ram from my 2nd pc to do some benchmarks.

Thanks for the contributions either way, as it's proved an interesting discussion.

@zanthor
that sounds about right

as for a 'path'... how about multiple cards within the same box to render different screens? maybe:

o quad core
o 3G RAM
o 2x512M nvidea cards
o 4x22" screens

that should allow you to quad box and probably get the fps you'd like (a cpu per game and 256M grfx ram per instance)

anyone try anything like this yet?