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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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