The limitation of your graphics card is not a simply answered question, as there's no across-the-board answer; it depends on the type of graphics card you own and the specifications of your computer. However, there are certain limitations to the way that graphics cards can access the CPU. This depends entirely on the build of the graphics card, and whether is has a dedicated graphics processing unit installed.
Graphic Card Types
There's more than one kind of graphics card – and not just in the sense that one has a DVI port and the other has HDMI. Some motherboards don't require a graphics card at all. It's expected that older and more basic computers have motherboards with built-in VGA or DVI ports for monitors; for casual computer users, that's rarely a problem. From there, you have basic graphics cards, which have some built-in RAM and more port options. High-end graphics cards are larger and more defined. These include cards that come with built-in fans, several gigabyes of RAM and GPU specifically designed for the task of rendering 3D graphics. Gamers and engineers are the most likely to need these more intense graphics cards.
Integrated Graphics and CPU
If your computer uses integrated graphics, this means that it shares the burden of video processing with your on-board RAM and your CPU – as opposed to video cards that have a GPU and dedicated RAM. While this solution is good for casual use, the performance of your game and your PC will decrease while running graphic-intensive games or tasks; many video-intensive programs may not render properly with integrated graphics.
The GPU takes the burden of rendering graphics of the CPU and is more specifically designed for the task of rendering 3D graphics. GPU is present in video cards that also have built-in RAM, so that when you run a game or video-intensive task, it pulls less from your system resources and more from the video card. This does not mean that the CPU is not used, just that it lightens the load overall.
GPU Versus CPU
GPUs actually have significantly more raw power than CPUs when used in certain applications, especially visual, mathematic and scientific applications. This variance ranges from 14 times more power than CPU in an Intel test and up to 100 times faster, according the Nvidia employees. That doesn't mean that the GPU could run your computer – in fact, most programs would require significant technical changes to run on a GPU. A part of this is because while a GPU excels at handling multiple tasks all at once as part of the necessity of rendering complex graphics, CPUs are designed to handle sequential tasks. High-end computers are built with both kinds of processing units, to handle both kinds of tasks with ease.
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