opengl - I stored more data on VRAM than it's actual size. How is that possible? -

i analysing performance of simple voxelized world renderer. wanted find performance limits different techniques, kind of stress test. @ point found wierd. allocating geometry data in chunks using different vbo each chunk. i'm using few counters programmed engine helped me see happening data.

here trying allocate 664 chunks containing 1 199 824 voxels altogether built using 28 795 776 vertices.
each vert consists of 3 floats position, 3 floats normal vector , 4 floats rgba color. float apparently 4 bytes of size, based on calculated estimated memory size of whole world 1098mb ( vertexcount * 3 * 4 * 2 + vertexcount * 4* 4).
i ran program fine @ amazing speed of 7 fps, worked , looked should. problem i'm using gigabyte geforce gtx 460 oc2 1 gb of video memory. how able allocate trough vbo 1098mb of data?
data cached of compressed somehow once inside vram?
or maybe there few mb of reserve memory had no idea about? explanation counters giving me wrong results or there don't know aobut video memory management?

what vram you're talking about? ;)

opengl has no concept of vram or graphics card local memory. there's "memory" in opengl, that's purely abstract. data can swapped gpu local memory system memory , needed.

if hardware supports (and gtx460 does!) textures can larger available gpu local memory , required texture subdata gets swapped in on demand.