No More Memory Bandwidth

Again, we have a 256 bit (4x 64 bit) memory interface to GDDR3 memory. The local graphics memory setup is not significantly different from the 6800 series of cards and only runs slightly faster at a 1.2 GHz effective data rate. This will work out in NVIDIA's favor as long as newer games continue to put a heavier burden on pixel shader processing. NVIDIA sees texture bandwidth as outweighing color and z bandwidth in the not too distant future. This doesn't mean the quest after ever increasing bandwidth will stop; it just means that the reasons we will need more bandwidth will change.

A good example of the changing needs of graphics cards is Half-Life 2. While the game runs very well even on older graphics cards like the 9800 Pro, the design is such that increased memory bandwidth is far less important than having more shader processing power. This is why we see the 6600GT cards significantly outperform the 9800 Pro. Even more interesting is that in our testing, we found that enabling 4xAA on a 9800 Pro didn't affect performance of HL2 much at all, while increasing the resolution from 1024x768 to 1280x1024 had a substantial impact on frame rates. If the HL2 model is a good example of the future of 3D engines, NVIDIA's decision to increase pixel processing power while leaving memory bandwidth for the future makes a lot of sense.

On an interesting side note, the performance tests in this article are mostly based around 1600x1200 and higher resolutions. Memory usage at 2048x1536 with 32bit color and z-buffer runs a solid 144MB for double buffered rendering with 4x AA. This makes a 256MB card a prerequisite for this setup, but depending on the textures, render targets and other local memory usage, 256MB may be a little short. PCI Express helps a little to alleviate any burden placed on system memory, but it is conceivable that some games could get choppier when swapping in and out large textures, normal maps, and the like.

We don't feel that ATI's 512MB X850 really brings anything necessary to the table, but with this generation we could start to see a real use for 512MB of local memory. MRTs, larger textures, normal maps, vertex textures, huge resolutions, and a lack of hardware compression for fp16 and fp32 textures all mean that we are on the verge of seeing games push memory usage way up. Processing these huge stores of data require GPUs powerful enough to utilize them efficiently. The G70 begins to offer that kind of power. For the majority of today's games, we are fine with 256MB of RAM, but moving into the future it's easy to see how more would help.

In addition to these issues, a 512MB card would be a wonderful fit for Dual-Link DVI. This would make the part a nice companion to Apple's largest Cinema Display (which is currently beyond the maximum resolution supported by the GeForce 7800 GTX). In case anyone is curious, a double buffered 4xAA 32bit color+z framebuffer at 2560x1600 is about 190MB.

In our briefings on G70, we were told that every part of the chip has been at least slightly updated from NV4x, but the general architecture and feature set is the same. There have been a couple of more significant updates as well, namely the increased performance capability of a single shader pipe and the addition of transparency antialiasing. Let's take a look at these factors right now.

The Pipeline Overview Inside The Pipes
POST A COMMENT

127 Comments

View All Comments

  • WaltC - Thursday, June 23, 2005 - link

    I found this remark really strange and amusing:

    "It's taken three generations of revisions, augmentation, and massaging to get where we are, but the G70 is a testament to the potential the original NV30 design possessed. Using the knowledge gained from their experiences with NV3x and NV4x, the G70 is a very refined implementation of a well designed part."

    Oh, please...nV30 was so poor that it couldn't even run at its factory speeds without problems of all kinds--which is why nVidia officially cancelled nV30 production after shipping a mere few thousand units. JHH, nVidia's CEO went on record saying, "nV30 was a failure" [quote, unquote] at the time. nV30 was [i]not[/i] the foundation for nV40, let alone the G70.

    Indeed, if anything could be said to be foundational for both nV40 and G70, it would be ATi's R3x0 design of 2002. G70, imo, has far more in common with R300 than it does nV30. nV30, if you recall, was primarily a DX8 part with some hastily bolted on DX9-ish add-ons done in response to R300 (fully a DX9 part) which had been shipping for nine months prior to nV30 getting out of the door.

    In fact, ATi owes its meteoric rise to #1 in the 3d markets over the last three years precisely to the R3x0 products which served as the basis for its later R4x0 architectures. Good riddance to nV3x, I say.

    I'm always surprised at the short and selective memories displayed so often by tech writers--really makes me wonder, sometimes, whether they are writing tech copy for their readers or PR copy at the behest of specific companies, if you know what I mean.
    Reply
  • JarredWalton - Thursday, June 23, 2005 - link

    98 - As far as I know, the power was measured at the wall. We use a device called "Kill A Watt", and despite the rather lame name, it gives accurate results. It's almost impossible to measure the power draw of any single component without some very expensive equipment - you know, the stuff that AMD and Intel use for CPUs. So under load, the CPU and GPU (and RAM and chipset, probably) are using far more power than at idle. Reply
  • PrinceGaz - Thursday, June 23, 2005 - link

    I agree, starting at 1600x1200 for a card like this was a good idea. If your monitor can only do 1280x1024, you should consider getting a better one before buying a card like the 7800gtx. As a 2070/2141 owner myself, I know that a good monitor capable of high resolutions is a great investment that lasts a helluva lot longer than graphics cards, which are usually worthless after four or five years (along with most other components).

    I'm surprised that no one has moaned about the current lack of an AGP version, to go with their Athlon XP 1700+ or whatever ;)
    Reply
  • Johnmcl7 - Thursday, June 23, 2005 - link

    I think it was spot on to have 1600x1200 as the minimum resolution, given the power of these cards I think 1024x768, no AA/AF results for 3Dmark2003/2005 which have been thrown around are a complete waste of time.

    John
    Reply
  • Frallan - Thursday, June 23, 2005 - link

    Good review... And re: the NDA deadlines and the sleapless nights - don't sweat it if a few mistakes are published. The readers here have their heads screwed on the right way and will find the issues for soon enough. And for everyone that does not do 12*16 or 15*20 the answer is simple - U Don't Need The Power!! Save your hard earnt money and get a 6800gt instead. Reply
  • Calin - Thursday, June 23, 2005 - link

    Maybe if you could save the game, change the settings and reload it you could obtain images from exactly the same positions. In one of the fence images, the distance to the fence is quite a bit different in different screenshots Reply
  • Calin - Thursday, June 23, 2005 - link

    You had an 7800 SLI? I hate you all
    :p
    Reply
  • xtknight - Thursday, June 23, 2005 - link

    Edit: last post correction: actually 21-page report! Reply
  • xtknight - Thursday, June 23, 2005 - link

    Jeez...a couple spelling errors here and there...who cares? I'd like to see you type up a 12-page report and get it out the door in a couple days with no grammatical or spelling errors, especially when your main editor is gone. Remember that English study that showed the human brain interpreted words based on patterns and not spelling?

    I did read the whole review, word-for-word, with little to no trouble. There was not a SINGLE thing I had trouble comprehending. It's a better review than most sites have done which test lower resolutions. I love the non-CPU-limited benchmarks here.

    One thing that made me chuckle was "There is clearly a problem with the SLI support in Wolfenstein 3D". That MS-DOS game is in dire need of SLI. (It's abbreviated Wolfenstein: ET. Wolf3D is an oooold Nazi game.)
    Reply
  • SDA - Thursday, June 23, 2005 - link

    Derek or Jarred or Wesley or someone:

    Did you measure system power consumption as how much power the computer drew from the wall, or how much power the innards drew from the PSU?


    #95, it's a good thing you know enough about running a major hardware site to help them out with your advice! :-)
    Reply

Log in

Don't have an account? Sign up now