A graphics card consists of a lot of components; one of the most important is the GPU. This is where all the advanced calculations are taking place. Basically, a GPU works the same way as a CPU. It gets some instructions it then handles. Their ways is separated pretty quickly though, because it is two very different kinds of instructions they have to handle. A GPU makes a lot of geometric calculations, because the graphics on your screen consists of billions of tiny triangles. Or, that is how it is in games and 3D. In 2D, the graphics card works in almost the same way as a TV. A signal is sent to the monitor, where the processor of the graphics card creates a picture, and that is a very simple picture. But in the same second as you put some advanced 3D graphics on the monitor, things happen. Instead of creating a very simple picture, the GPU now has to create a lot of triangles.
Just as a CPU, a GPU runs at a certain speed. Where a modern 4-cored CPU runs at 3.5 GHz, a 1.536-cored GPU only runs at 950 MHz, but that is for every single core. 950 multiplied with 1.536 gives a totally insane number. A graphics card’s speed is measured in the unit “FLOPS”. FLOP is short for: “Floating Points Operations Per Second”, and indicates how many calculations a given graphics card can totally handle per second. Modern graphics cards have a total processing power of up to 3-4 teraflops. That is very, very much, and counts dual-GPU graphics cards, which is a melt of two graphics cards to one, only.
A 3D game works the way that everything is built up from triangles, and it is the graphics cards task to change the triangle’s shape and colour, and change the colours the triangle contains. This task is so demanding that you won’t believe it. That is one of the reasons, why a modern GPU consists of more than 1.500 cores. There is a lot of processing power required. That is one of the reasons why a CPU fails when it has to create 3D. A modern CPU has 4-8 cores only, which obviously isn’t enough. The more cores a graphics card has, the better graphics it creates.
Something else that plays a role is of course the resolution. If I take the resolution 1920 * 1080 it gives me 2.073.600 pixels or circa 2 megapixels. 2 megapixels does not sound like a lot, but really, really many triangles have to be made before it makes sense. If I then take a resolution of 2560 * 1440 it gives 3.686.400 pixels or almost 4 megapixels. That is 77 % more pixels than 1920 * 1080, which results in a much heavier task for the GPU. I will not talk about ROPs etc. here, as it quickly becomes nonsense.