Please help demystify Vid Card onboard RAM

[dieselfrog]

Like many others on this board I?m in the position of having to choose between two mid-market vid cards. I'm building a new rig from the ground up and my new MoBo supports PCI-e. The cards I?m choosing between are the x700 PRO and the 6600 GT.

Now, before you get your panties in a bunch, i've done my homework (search) and I know that the question of "which is better?" has been answered many (many) times on in these forums with the 6600 GT coming out as the undisputed middle weight champion. The thing I wonder about is the differences in vid RAM.

The x700 PRO has 256mb and the GT has 128. I understand that it is the speed of the RAM that makes the 128 of the GT more desireable. Is that correct?

What exactly does the RAM on the vid cards get you? Where would you normally see the boost or advantage of picking a card with higher ram? Do you guys foresee game makers utilizing the vid card more thus making the higher RAM capacity cards more desirable than the smaller, faster RAM configurations?

Thanks for helping to shed some light on this somewhat confusing subject. All of us n00bs that assume that bigger is always better thank you for your enlightenment.

 

[Cerb]

RAM is needed for textures. There is a switching* total of 15+GB/s bandwidth in a typical card. Your system RAM is most likely PC3200, getting 3.2GB/s. When the video card has to swap small amounts of textures out, you don't notice it. If you don't have enough video RAM to hold the needed textures, though, it has to flush some back to system memory, and then get some others from system memory.

So it goes from video card -> AGP interface -> memory controller -> RAM, then back again.
It is not terribly fast (PCI-E should help a bit, there, but currently Doom3 and HL2, card killers, are the only games able to really use more than 256MB, so testing wouldn't be conclusive), and can cause stuttering.

The solution: more RAM. However, that costs, which is one reason why the prices go up so, and why Geforce 5x00 and Radeon 9x00 prices haven't gone down much at the high end.

Aside: often, 128MB cards are faster, because the 256MB cards use cheaper, slower, RAM.

A 256MB card will get you a bit more longevity, but is generally considered not worth it, as the tech always gets cheaper for the performance. Might as well save $100 now, if you won't use it, and consider that put towards the new card in 1-3 years.

* - modern cards have several channels of SDRAM. Rather than having a synchronous quad-channel, FI, each channel is accessed separately, and dealt with much like (but with more complexity than) a network switch, since each piece of data requested tends to be small.

 

[LTC8K6]

Basic rule, 256MB (or more) of video ram is useless except on the very top end cards at the highest resolutions.

256MB of ram on the midddle and low end cards is pure marketing. They cannot take advantage of the ram because they are not fast enough in the first place.

 

[carlosd]

Originally posted by: LTC8K6
Basic rule, 256MB (or more) of video ram is useless except on the very top end cards at the highest resolutions.

256MB of ram on the midddle and low end cards is pure marketing. They cannot take advantage of the ram because they are not fast enough in the first place.