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RAM Bandwidth Versus Quantity

How Much RAM Does Your Graphics Card Really Need?
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The biggest misconception out there is that more graphics RAM will increase gaming performance. But, for the most part, this is untrue. While the bandwidth of the graphics RAM might have a direct effect on gaming performance, the quantity of RAM doesn't have a direct impact on how fast a graphics card performs. The quantity of RAM does have an indirect impact on performance sometimes, and we'll talk about this in a little bit.

The bandwidth of graphics card RAM is affected by two main factors: the clock rate and interface width. Clock rate is measured in MHz, just like a CPU. The width of an interface is measured in bits, such as 128-bits wide. Without going into too much detail, you should know that 200 MHz memory should provide twice the bandwidth of 100 MHz memory, assuming everything else is equal. Similarly, a 128-bit memory bus should provide twice the bandwidth of a 64-bit bus.

It gets a little complicated because we're talking about two variables here: clock rates and bandwidth. For example, 200 MHz, 64-bit memory should offer approximately the same bandwidth as 100 MHz, 128-bit memory. There are other factors, such as memory latency. Technology also plays a role, as GDDR5 offers twice the throughput of DDR through GDDR4 at a given clock speed. But, for the most part, all you have to remember is that more bandwidth should have a direct impact on your gaming performance.

However, we won't look too hard at memory bandwidth today. Instead, the quantity of graphics card RAM is what we'll focus on, which is measured in megabytes (MB) or gigabytes (GB).

As we've said, the quantity of RAM that the graphics card employs doesn't have a direct impact on game performance, but it can have an indirect impact. Graphics card RAM will only negatively affect performance if there isn't enough to handle what a specific game title requires. The point is that all other factors being equal, a graphics card with 2GB (2,048 MB) should perform exactly the same as a graphics card with 512MB as long as the game's graphics memory requirements are below 512MB. If the game's settings and resolution require more than 512MB of graphics card RAM, the 512MB card will demonstrate a performance penalty compared to the 2GB card.

With this in mind, we're going to see exactly what happens when we test a number of popular games at different settings and resolutions with three different graphics cards armed with 512MB, 1GB, and 2GB of RAM. All of these models center on ATI's Radeon HD 4870 GPU, and we will make sure they are set to the same clock speeds so that the bandwidth and engine throughput are identical. Let's have a quick look at the cards.

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  • 39 Hide
    burnley14 , October 1, 2009 3:20 AM
    I really like the alternating images you use in these articles, they are very helpful and make it much easier to compare the various detail settings.

    Also, great article overall. Keep up the good work!
  • 33 Hide
    cleeve , October 1, 2009 3:36 AM
    Thanks burnley, animated GIFs are a bit of a pain to make, but it's nice to know they're appreciated. :) 
  • 19 Hide
    cleeve , October 1, 2009 4:00 AM
    knutjbHow much ram will the 5870 eyefinity version need?


    Depends on the resolution and settings just like everything else. but it's a good question, if there's enough interest in this article I'll look into that in the future.
Other Comments
  • 9 Hide
    radiowars , October 1, 2009 3:13 AM
    Great article guys. I've debated this many times with friends- good to see a definite result. Heh, GTX 275 w/ 896 works well @ 1680x1050 for me. I doubt I'd need anything higher than that for my resolution.
  • 39 Hide
    burnley14 , October 1, 2009 3:20 AM
    I really like the alternating images you use in these articles, they are very helpful and make it much easier to compare the various detail settings.

    Also, great article overall. Keep up the good work!
  • 33 Hide
    cleeve , October 1, 2009 3:36 AM
    Thanks burnley, animated GIFs are a bit of a pain to make, but it's nice to know they're appreciated. :) 
  • 0 Hide
    blueer03 , October 1, 2009 3:48 AM
    This was very interesting. But I would like to see the performance difference from a mid-stream (say a 4850) as compared to a high end video card. Would it have made sense to spring for the 1GB 4850, or would there be no difference because of the cards inherent limitations? And the same thing with the lower level cards. At what point in the hierarchy of video cards does springing for more than the reference memory levels make sense?
  • 4 Hide
    cleeve , October 1, 2009 3:57 AM
    With lower end cards you'd see the same effect, but with the lower frame-rates that those cards would produce. The end result is the same: one they run out of RAM at a certain setting, the performance will suffer, but until then it's the same across the board.
  • 3 Hide
    knutjb , October 1, 2009 3:58 AM
    How much ram will the 5870 eyefinity version need?
  • 19 Hide
    cleeve , October 1, 2009 4:00 AM
    knutjbHow much ram will the 5870 eyefinity version need?


    Depends on the resolution and settings just like everything else. but it's a good question, if there's enough interest in this article I'll look into that in the future.
  • 2 Hide
    liquidsnake718 , October 1, 2009 4:11 AM
    Im surprised that Crysis doesnt utilize all the RAM(even for an older title) for distance similarly to titles like GTA. Im sure the new Crytek engine will make use of Ram so we can see even buildings and huge alien robots further in the distance with vivid details.

    We can only look forward to a more intense and visually stunning Crysis 2 as I can only imagine how the story would progress and end up being in space. I can imagine huge asteroids looking as real coming at the player using nvidias 3d vision and utilizing AA in order to make it apparent from a distance.

    Think Halo style world but with unrivaled graphics and a more realistic feel with DX11.
  • 11 Hide
    Anonymous , October 1, 2009 4:28 AM
    How about doing this same comparison with crossfire setups?
  • -8 Hide
    Arkz , October 1, 2009 4:29 AM
    il tell ya whats a bitch, i have a 1920x1080 monitor, nice? yes. I have an 8800GT too.. nice? kinda.. its the 256MB version.. so.. if i wanna turn up the sexiness i get baaaad fps
  • 2 Hide
    HibyPrime , October 1, 2009 4:30 AM
    Would have been nice to see more of the GTA4 benches, as it's pretty safe to say it requires the most video ram of current gen games.

    Slowly increase the ram from the 500mb point to see where the 512 cuts out. Maxing out all of the sliders to see if the 2GB is ever able to make a win over the 1GB as well as showing the visual difference from the 1GB up to whatever the max is.
  • 1 Hide
    tjf311 , October 1, 2009 4:32 AM
    What if I wanted to run in crossfire? What would be the optimal configuration then? 2x? 3x? 4x?
  • 1 Hide
    Shnur , October 1, 2009 4:32 AM
    Great article!
    I am actually looking forward a 5870 (or nVidia next-gen if it comes in this year) after prices are settled and early drivers are out of the way so I can really see an improvement over my 4870 1gb. This is the kind of article I wanted to see for a while and I give you guys a big heads up for it! It would be nice at a later time to see with the new cards how does 2gb vs 1gb performs when paired in CF/SLI so we can eliminate the card speed factor that we have here, because even if the game would like to use more ram, the card is not fast enough to process the information, when you get two cards, there's more power as for processing but same storage, that would be a great thing to check :) 
    And I'm looking forward an eyefinity review with a game running on 3 HD screens or something similar because as of today an HD screens costs about 200$ so buying two or three is expensive but still on the level of "affordable" when a single 30" is more expensive than this...
  • 2 Hide
    Supertrek32 , October 1, 2009 4:34 AM
    CleeveThanks burnley, animated GIFs are a bit of a pain to make, but it's nice to know they're appreciated.

    It's a very nice thing to have. I wish more benchmarks on Tom's had these, since I'm reading to find out what I want to buy. It's great for figuring out if the next card is worth it for that next step up.

    It answers the "Yeah, I could use very-high instead of regular-high with this card instead of that, but will I even be able to tell the difference?" question.
  • 2 Hide
    megamanx00 , October 1, 2009 4:35 AM
    Indeed 2GB is rather frivolous right now. Given current prices I'd really recommend a 1GB 4870 over a 512MB 4870. GRID and FarCry2 are games that currently favor 1GB, and I'm sure we'll see more this fall.
  • 5 Hide
    eddieroolz , October 1, 2009 4:45 AM
    Great article, very well written and informational.
  • 0 Hide
    WINTERLORD , October 1, 2009 4:46 AM
    great article. and good to know. all this graphics stuff latly makes me wanna upgrade lol. that and i have a new favorite game. intersting to say the least, and from looking at this, i would definatly get atleast a 1gb card in the future. since games are always changing like the editor said, i believe that when directx 11 comes out and 2 years down the road, that you would definatly want 1gb of ram on your card. but seems like 512 would be good for a good long time as well
  • 0 Hide
    IzzyCraft , October 1, 2009 5:19 AM
    The more the better as long as the gpu and setup can use all of it. Seems like 1 gig is a norm now and a good apart for those who are cranking up the AA and AF and resolution esp if that AA is super-sampling.
  • 4 Hide
    porksmuggler , October 1, 2009 5:19 AM
    excellent article, nice overview of a frequently debated issue.
  • 0 Hide
    intelx , October 1, 2009 5:21 AM
    very good article, saving money with the same speed.
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