The Myths Of Graphics Card Performance: Debunked, Part 1

The Myths Surrounding Graphics Card Memory

Video memory enables resolution and quality settings, does not improve speed

Graphics memory is often used by card vendors as a marketing tool. Because gamers have been conditioned to believe that more is better, it's common to see entry-level boards with far more RAM than they need. But enthusiasts know that, as with every subsystem in their PCs, balance is most important.

Broadly, graphics memory is dedicated to a discrete GPU and the workloads it operates on, separate from the system memory plugged in to your motherboard. There are a couple of memory technologies used on graphics cards today, the most popular being DDR3 and GDDR5 SDRAM.

Myth: Graphics cards with 2 GB of memory are faster than those with 1 GB

Not surprisingly, vendors arm inexpensive cards with too much memory (and eke out higher margins) because there are folks who believe more memory makes their card faster. Let's set the record straight on that. The memory capacity a graphics card ships with has no impact on that product's performance, so long as the settings you're using to game with don't consume all of it.

What does having more video memory actually help, then? In order to answer that, we need to know what graphics memory is used for. This is simplifying a bit, but it helps with:

  • Loading textures
  • Holding the frame buffer
  • Holding the depth buffer ("Z Buffer")
  • Holding other assets that are required to render a frame (shadow maps, etc.)

Of course, the size of the textures getting loaded into memory depends on the game you're playing and its quality preset. As an example, the Skyrim high-resolution texture pack includes 3 GB of textures. Most applications dynamically load and unload textures as they're needed, though, so not all textures need to reside in graphics memory. The textures required to render a particular scene do need to be in memory, however.

The frame buffer is used to store the image as it is rendered, before or during the time it is sent to the display. Thus, its memory footprint depends on the output resolution (an image at at 1920x1080x32 bpp is ~8.3 MB; a 4K image at 3840x2160x32 is ~33.2 MB), the number of buffers (at least two; rarely three or more).

As specific anti-aliasing modes (FSAA, MSAA, CSAA, CFAA, but not FXAA or MLAA) effectively increase the number of pixels that need to be rendered, they proportionally increase overall required graphics memory. Render-based anti-aliasing in particular has a massive impact on memory usage, and that grows as sample size (2x, 4x, 8x, etc) increases. Additional buffers also occupy graphics memory.

So, a graphics card with more memory allows you to:

  1. Play at higher resolutions
  2. Play at higher texture quality settings
  3. Play with higher render-based antialiasing settings

Now, to address the myth.

Myth: You need 1, 2, 3, 4, or 6 GB of graphics memory to play at (insert your display's native resolution here).

The most important factor affecting the amount of graphics memory you need is the resolution you game at. Naturally, higher resolutions require more memory. The second most important factor is whether you're using one of the anti-aliasing technologies mentioned above. Assuming a constant quality preset in your favorite game, other factors are less influential.

Before we move on to the actual measurements, allow me to express one more word of caution. There is a particular type of high-end card with two GPUs (AMD's Radeon HD 6990 and 7990, along with Nvidia's GeForce GTX 590 and 690) that are equipped with a certain amount of on-board memory. But as a result of their dual-GPU designs, data is essentially duplicated, halving the effective memory. A GeForce GTX 690 with 4 GB, for instance, behaves like two 2 GB cards in SLI. Moreover, when you add a second card to your gaming configuration in CrossFire or SLI, the array's graphics memory doesn't double. Each card still has access only to its own memory.

These tests were run on a Windows 7 x64 setup with Aero disabled. If you’re using Aero (or Windows 8/8.1, which doesn't have Aero), you should add ~300 MB to each and every individual measure you see listed below.

As you can see from the latest Steam hardware survey, most gamers (about half) tend to own video cards with 1 GB of graphics memory, ~20% have about 2 GB, and the number of users with 3 GB or more is less than 2%.

We tested Skyrim with the official high-resolution texture pack enabled. As you can see, 1 GB of graphics memory is barely enough to play the game at 1080p without AA or with MLAA/FXAA enabled. Two gigabytes will let you run at 1920x1080 with details cranked up and 2160p with reduced levels of AA. To enable the full Ultra preset and 8xMSAA, not even 2 GB card is sufficient.

Bethesda’s Creation Engine is a unique creature in this set of benchmarks. It is not easily GPU-bound, and is instead often limited by platform performance. But in these tests, we newly demonstrate how Skyrim can be bottlenecked by graphics memory at the highest-quality settings.

It's also worth noting that enabling FXAA uses no memory whatsoever. There's a value trade-off to be made in cases where MSAA is not an option.

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135 comments
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    Top Comments
  • blackmagnum
    Myth #123: Gamers are lonely boys in Mother's dark basement or attic...
    27
  • cats_Paw
    Awsometacular article.Not only its a new standard for GPU performance, but the Human Benchmark and audio test was really fun!Im normally very critisizing about toms articles becouse many times they feel a bit weak, but this one?10/10
    16
  • Jaroslav Jandek
    Quote:
    The info on V-Sync causing frame rate halving is out of date by about a decade. With multithreading the game can work on the next frame while the previous frame is waiting for V-Sync. Just look at BF3 with V-Sync on you get a continous range of FPS under 60 not just integer multiples. DirectX doesn't support triple buffering.
    The behavior of V-Sync is implementation-specific (GPU drivers/engine). By using render ahead, swap chains, Adaptive V-Sync, etc., you can avoid frame halving.

    DirectX DOES support TB by using DXGI_SWAP_CHAIN_DESC.BufferCount = 3; (or D3DPRESENT_PARAMETERS.BackBufferCount = 2; for DX9). It actually supports more than triple buffering - Direct3D 9Ex (Vista+'s WDDM) supports 30 buffers.
    12
  • Other Comments
  • manwell999
    The info on V-Sync causing frame rate halving is out of date by about a decade. With multithreading the game can work on the next frame while the previous frame is waiting for V-Sync. Just look at BF3 with V-Sync on you get a continous range of FPS under 60 not just integer multiples. DirectX doesn't support triple buffering.
    -11
  • ingtar33
    awesome article, looking forward to the next half.
    5
  • blackmagnum
    Myth #123: Gamers are lonely boys in Mother's dark basement or attic...
    27
  • AlexSmith96
    Great Article! I love you guys for coming up with such a nice idea.
    4
  • hansrotec
    with over clocking are you going to cover water cooling? it would seem disingenuous to dismiss overclocking based on a generating of cards designed to run up to maybe a speed if there is headroom and not include watercooling which reduces noise and temperature . my 7970 (pre ghz editon) is a whole different card water cooled vs air cooled. 1150 mhz without having to mess with the voltage on water with temps in 50c without the fans or pumps ever kicking up, where as on air that would be in the upper 70s lower 80s and really loud. on top of that tweeking memory incorrectly can lower frame rate
    2
  • hansrotec
    I thought my last comment might have seemed to negative, and i did not mean it in that light. I did enjoy the read, and look forward to more!
    6
  • hansrotec
    I thought my last comment might have seemed to negative, and i did not mean it in that light. I did enjoy the read, and look forward to more!
    -1
  • noobzilla771
    Nice article! I would like to know more about overclocking, specifically core clock and memory clock ratio. Does it matter to keep a certain ratio between the two or can I overclock either as much as I want? Thanks!
    -1
  • chimera201
    I can never win over input latency no matter what hardware i buy because of my shitty ISP
    5
  • immanuel_aj
    I'd just like to mention that the dB(A) scale is attempting to correct for perceived human hearing. While it is true that 20 dB is 10 times louder than 10 dB, but because of the way our ears work, it would seem that it is only twice as loud. At least, that's the way the A-weighting is supposed to work. Apparently there are a few kinks...
    -1
  • FunSurfer
    On Page 3: "In the image below" should be "In the image above"
    0
  • Formata
    "Performance Envelope" = GeniusNice work Filippo
    -1
  • beetlejuicegr
    I just want to mention that db is one thing, health of gpu over time is another. In many cases i have seen graphic cards going up to 90C before the default driver of ATI/Nvidia start to throttle down. i prefer a 50C-70C scenario
    -1
  • cats_Paw
    Awsometacular article.Not only its a new standard for GPU performance, but the Human Benchmark and audio test was really fun!Im normally very critisizing about toms articles becouse many times they feel a bit weak, but this one?10/10
    16
  • ubercake
    What's up with Precision X? It seems like they would update it every couple of months and now there hasn't been an update since last June or July?Is EVGA getting out of the utility software business?
    0
  • kzaske
    Its' been a long time since Tom's Hardware had such a good article. Very informative and easy to read. Thank you!
    8
  • ddpruitt
    Very good article even though there are some technical errors. I look forward to seeing the second half! I would also be interesting in seeing some detailed comparisons of the same cards with different amounts and types of VRAM and case types on the overall impact of performance.
    -1
  • Jaroslav Jandek
    Quote:
    The info on V-Sync causing frame rate halving is out of date by about a decade. With multithreading the game can work on the next frame while the previous frame is waiting for V-Sync. Just look at BF3 with V-Sync on you get a continous range of FPS under 60 not just integer multiples. DirectX doesn't support triple buffering.
    The behavior of V-Sync is implementation-specific (GPU drivers/engine). By using render ahead, swap chains, Adaptive V-Sync, etc., you can avoid frame halving.

    DirectX DOES support TB by using DXGI_SWAP_CHAIN_DESC.BufferCount = 3; (or D3DPRESENT_PARAMETERS.BackBufferCount = 2; for DX9). It actually supports more than triple buffering - Direct3D 9Ex (Vista+'s WDDM) supports 30 buffers.
    12
  • Adroid
    I would love to see a Tom's article on debunking the 2GB vs 4GB graphic card race. For instance, people spam the Tom's forum daily giving advice to buy the 4GB GTX 770 over the 2GB. Truth is, the 4 GB costs 50$ more and offers NO benefit over the 2GB. Even worse, I see people buying/suggesting the 4GB 760 over a 2GB 770 (which runs only 30$ more and is worth every penny). I am also curious about the 4GB 770 sli scenario. For everything I have seen, even in Sli the 4GB offers no real-world benefit (with the exclusion of MAYBE a few frames per second higher at 3 monitor scenarios, but the rates are unplayable regardless so the gain is negligible). The other myth is that the 4GB 770 is more "future proof". Give me a break. GPU and future proof do not belong in the same sentence. Further, if they were going to be "future proof" they would be "now proof". There are games that are plenty demanding to show the advantage of 2gb vs 4gb - and they simply don't. It's tiring seeing people giving shoddy advice all over the net. I wish a reputable website (Tom's) would settle it once and for all. In my opinion, the extra 2 GB of RAM isn't going to make a tangible difference unless the GPU architecture changes...
    8
  • ubercake
    DisplayLag.com lists 120Hz and 240Hz HDTVs amongst the monitors, but the maximum input speed for the HDTVs' inputs equate to 60fps? Or am I missing something?If I buy a 240Hz refresh TV, that's output. It processes the 60Hz signal to transform it to a 240Hz output (usually through some form of frame duplication) to minimize motion blur. Does this displayLag.com site mentioned in the article compare apples to oranges by listing HDTVs with monitors as if they operate the same way or am I way off here?
    0