The case for using system RAM
Obviously, the point of TurboCache is to allow higher-performance graphics at lower prices. NVIDIA points out all sorts of graphics geeky reasons why the time is right for TurboCache to exist. I'll try sum them up in three points. First, of course, is the advent of PCI Express and the additional bandwidth it provides, especially the bandwidth coming back from the GPU into main memory, which was problematic with AGP. Second, games are now using more memory than ever for renderable surfaces, all of which requires storage space. 128MB is commonly required for best quality by some newer games, and 256MB is the next milestone. The ability to allocate a portion of system RAM for graphics should help enable cheaper graphics solutions to handle these more demanding applications. Third, although memory space requirements are growing, NVIDIA says programmable shading is reducing the need for memory bandwidth. Since real-world bandwidth and latency are interrelated, this point is important, even though we've been throwing around some relatively big numbers for total peak theoretical memory bandwidth in a 6200 with TurboCache config. Here's a quick summary NVIDIA provided to illustrate how programmable shaders might cut the need for memory bandwidth versus traditional multipass rendering.

Of course, this is a very extreme example, but it makes the point. Programmable shading is reducing bandwidth pressure for color and Z writes (this is also the reason why the NV44 can live with only two ROPs). Examples like this one will be more pertinent as programmable shading becomes more prevalent.

NVIDIA says TurboCache offers better overall system performance than an integrated chipset graphics solution, and that makes sense, given the fact that the 6200 has local frame buffer to handle non-3D display tasks. The company also claims TurboCache is ideal for laptops, because fewer RAM chips onboard will allow for reduced power consumption.

In fact, the folks at NVIDIA so believe in the TurboCache scheme that they have no apparent plans for a future GeForce 6200 solution that doesn't use it. The current, NV43-derived GeForce 6200 will eventually die off. One place where TurboCache will not prevail is on AGP systems, where the GeForce FX line will continue as NVIDIA's low-end solution.

We have been hearing for a while now about a new virtual memory hierarchy coming for graphics, possibly along with Microsoft's Longhorn OS. Obviously, TurboCache is a big step in that direction, although it's not quite the whole enchilada. When asked about the possibility of seeing TurboCache used on higher-end card, as a means of augmenting their larger pools of local RAM, NVIDIA said to "stay tuned." They also were quick to talk down the prospects for ATI's competing HyperMemory technology, claiming it will only be the equivalent of AGP texturing and nothing more. We'll have to see about that.

The selling of TurboCache
One of the more sensitive issues NVIDIA will have to address will be how to sell the GeForce 6200 with TurboCache. Feisty consumers may not like the sound of a graphics card with only 16MB or 32MB of memory, so NVIDIA and its partners will need to sell these cards confidently without being deceptive. NVIDIA offered us a look at a product box mock-up with some carefully worded language about the GeForce 6200 graphics card "supporting 128MB." The fine print on the box includes a quick description of the TurboCache memory sharing scheme and notes that 512MB of memory is required to get "full 128MB support." All of this is well and good, but the actual amount of local memory on the board is completely omitted in NVIDIA's example. Likewise, NVIDIA's first drivers for the 6200 with TurboCache simply show a 128MB graphics device, with no notation of the amount of memory actually on the card.

I understand the need to sell this solution to wary consumers in an appropriate manner, but I expect NVIDIA and its partners will have to give a little here. The performance difference between a one-chip/16MB and two-chip/32MB 6200 with TurboCache is notable, and folks will want to be able to determine which version of the card they're getting. NVIDIA partners may also choose to introduce cards with denser 32MB DRAM chips, and they'll want to tell the world about the extra local frame buffer space.