Virtual Memory

Microsoft is taking tighter control of graphics memory with it's new driver model, and thus is able to provide virtual memory support for the graphics memory subsystem. What this means is that games no longer need to worry about running out of graphics memory. When software needs to write something to local memory, and local memory is full, Windows will be able to kick out something off the graphics card and put it in system memory (this is called paging) until it is needed. This happens without the software's intervention or knowledge. If system memory becomes full, data will be kicked out to the hard drive. Of course, if something like this happens the performance will definitely suffer.

Virtual memory isn't as much a performance enhancing tool as it is a way to remove the burden on the developer to manage memory usage around a hard limit of available space. Certainly, lots of paging will degrade performance, but lower performance is generally better than a crash. On the flip side, it is possible that virtual memory could increase performance by effectively replacing local graphics memory size with unused PCIe bandwidth. This has been the idea behind TurboCache and HyperMemory, but with the added advantage that the graphics driver doesn't need to worry about object or texture management between local and system memory.

Engineers have been wanting to see virtualized graphics memory for years, as operating on really huge data sets is made significantly easier when the software developer doesn't have to manage moving data in and out of graphics memory by hand. We've seen some limited benefits of utilizing both local and system memory on low memory TurboCache and HyperMemory cards. With game developers reaching towards ever larger data sets, high end parts will soon begin to benefit from virtualized graphics memory as well. Building the hardware to accommodate the possibility of higher latencies due to paging and allowing the OS to manage all the memory in the system will definitely help developers focus on building better games rather than better memory managers. That's not to say that memory management won't still be important to game developers. Making sure space and bandwidth are used efficiently are important factors in performance, but the ability to forget about hard limits in local memory will make it easier to take one efficient approach regardless of onboard memory.

Hardware Virtualization

Lately, all the big boys of computing have been infatuated with the idea of virtualization. It makes a whole lot of sense, really. With the advent of multi-core CPUs, AMD and Intel need to find ways to take full advantage of their processing power. Single thread execution time will never disappear as a factor in computing, and some algorithms just can't be parallelized.

Obviously, encouraging users to multitask is a simple way to provide a benefit to multi-core computing. The next step is to encourage developers to write highly multithreaded applications. Beyond that is to allow the user to run multiple operating systems on one set of hardware. One example of how this may be beneficial is in the use of a single system as a normal PC during its use as a home theater / DVR box. Another example is one we've already seen: Mac users running both Windows and OS X on Intel based Macs using a virtual machine manager like Parallels.

In order to really achieve the capabilities hardware providers would like to promote, more work must be done by hardware, software, and operating system providers. One of the major advances necessary is the virtualization of the graphics subsystem. With DirectX10 and the new WDDM (Windows Display Driver Model), graphics hardware is required to support virtualization. This is not a simple request, as games will no longer be guaranteed exclusive access to the hardware while running. We can potentially share game rendering with something like physics calculations on the same GPU. Or we could run a Folding@Home GPU client in the background while we play a game. On the extreme, multiple full screen 3d applications could be running concurrently.

Drivers and hardware will have to support context switching on a massive scale due the huge number of pipelines and registers supported in DX10 class hardware. With the advent of features like TurboCache and HyperMemory (and now graphics memory virtualization), hardware developers are already prepared to handle much larger latencies than we've seen in the past. The ability to preempt a process on the GPU will only increase the potential latency that will need to be addressed.

This is another major step in bringing the GPU closer in functionality to the CPU. More attention must be paid not only to instruction and thread scheduling, but the scheduling of multiple programs. This is no small task when such a high number of pipelines need to be managed. We are very interested in discovering how well NVIDIA has implemented this feature, but we won't be able to test this until we have access to an operating system, API, and software that support it as well.

Index All GPUs are Created Equal: Say Goodbye to Cap Bits
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  • yyrkoon - Thursday, November 09, 2006 - link

    If you're using Firefox, get, and install the extension "flashblock". Just did this myself today, tired of all the *animated* adds bothering me while reading articles.

    Sorry AT guys, but we've had this discussion before, and its realy annoying.
    Reply
  • JarredWalton - Thursday, November 09, 2006 - link

    Do you want to be able for us to continue as a site? Because ads support us. Anyway, his problem is related to not seeing images, so your comment about blocking ads via flashblock is completely off topic. Reply
  • yyrkoon - Thursday, November 09, 2006 - link

    Of course I want you guys to continue on as a site, just wish it were possible without annoying flashing adds in a section where I'm trying to concentrate on the article.

    As for the off topic part, yeah, my bad, I mis-read the full post (bad habit). Feel free to edit or remove that post of mine :)
    Reply
  • archcommus - Thursday, November 09, 2006 - link

    What browser are you using? Reply
  • falc0ne - Thursday, November 09, 2006 - link

    firefox 2.0 Reply
  • JarredWalton - Thursday, November 09, 2006 - link

    If Firefox, I know there's an option to block images not on the originating website. In this case, images come from image.anandtech.com while the article is on www.anandtech.com, so that my be the cause of your problems. IE7 and other browsers might have something similar, though I haven't ever looked. Other than that, perhaps some firewall or ad blocking software is to blame - it might be getting false positives? Reply
  • archcommus - Thursday, November 09, 2006 - link

    Wow to Anandtech - another amazing, incredibly in-depth article. It is so obvious this site is run by dedicated professionals who have degrees in these fields versus most other review sites where the authors just take pictures of the product and run some benches. Articles like this keep the AT reader base very very strong.

    Also wow to the G80, obviously an amazing card. My question, is 450W the PSU requirement for the GTX only or for both the GTX and GTS? I ask because I currently have a 400W PSU and am wondering if it will be sufficient for next-gen DX10 class hardware, and I know I would not be buying the highest model card. I also only have one HDD and one optical drive in my system.

    Yet another wow goes out to the R&D monetary investment - $475 million! It's amazing that that amount is even acceptable to nVidia, I can't believe the sales of such a high end, enthusiast-targeted card are great enough to warrant that.
    Reply
  • JarredWalton - Thursday, November 09, 2006 - link

    Sales of the lower end parts which will be based off G80 are what make it worthwhile, I would guess. As for PSU, I think that 450W is for the GTX, and more is probably a safe bet (550W would be in line with a high-end system these days, although 400W ought to suffice if it's a good quality 400W). You can see that the GTX tops out at just under 300W average system power draw with an X6800, so if you use an E6600 and don't overclock, a decent 400W ought to work. The GTX tops out around 260W average with the X6800, so theoretically even a decent 350W will work fine. Just remember to upgrade the PSU if you ever add other components. Reply
  • photoguy99 - Thursday, November 09, 2006 - link

    I just wanted to second that thought -

    AT articles have incredible quality and depth at this point - you guys are doing great work.

    It's actually getting embarrasing for some of your competing sites, I browsed the Tom's article and it had so much fluff and retread I had to stop.

    Please don't forget the effort is noticed and appreciated.
    Reply
  • shabby - Wednesday, November 08, 2006 - link

    It wasnt mentioned in the review, but whats the purpose of the 2nd sli connector? Reply

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