“GDDR6X does come with one somewhat immediate drawback however: capacity. While Micron has plans for 16Gbit chips in the future, to start things out today they’re only making 8Gbit chips in the future. This is the same density as the memory chips on NVIDIA’s RTX 20 series cards, and their GTX 1000 series cards for that matter. So there are no “free” memory capacity upgrades, at least for these initial cards. RTX 3080 only gets 10GB of VRAM versus 8GB on RTX 2080, and that’s by virtue of using a larger 320-bit memory bus (which is to say, 10 chips instead of 8). Meanwhile RTX 3090 gets 24GB of VRAM, but only by using 12 pairs of chips in clamshell mode on a 384-bit memory bus, making for more than twice as many memory chips as on RTX 2080 Ti.”


https://www.anandtech.com/show/16057/nvidia-announces-the-geforce-rtx-30-series-ampere-for-gaming-starting-with-rtx-3080-rtx-3090