You may have noticed that according to a number of signs, a video card is obtained by a separate computer inside a computer. The cards have their own BIOS, a separate set of memory, their own power circuits and, of course, their own processor, albeit a graphic one. It is easy to guess that they have similar and different features with the central processor, but they need to communicate: it is the central processor that commands the video card.
Therefore, for interaction, the processor often places copies or data cache in RAM for working with a video card. Plus, it is from the RAM that it transfers such information to the card via the PCI bus.
And since modern software, operating systems and processors began to work with 64-bits, then it is already necessary to manage much more space. Those. when moving from 32-bit, where there was a limit of only 4 gigabytes of data, now hardware and software can handle much larger values at once (in theory, up to 16 exabytes, in existing hardware implementations there are only 256 terabytes).