ang kanagn 512Mb, AND 1024Mb is the data size of your VRAM altogether. ang kanang 64 bit, 128 bit, and other are all called buswidth. It carries data of a 64-bit or any buswidth size per cycle sa usa ka lane. the memory-bus is what connects your GPU and VRAM. The higher the buswidth, the better performance.
SIMPLE LOGIC (EDITED)
Try thinking the GPU as one side of a river and the other side which is your VRAM. The memory bus is a ferry that does rounds to transport people from one side to the other. so if 64-bit ra xa, then 64 ra ka tawo iyang maferry at one instance then another 64 to ferry at the other side. the same principle is applied to the other buswidths. so if mas dako ang ferry, mas-dakodako imong data fetching and transferring.
