i was wondering why today's gpu have such a large frame buffer ( 1 GB) when they only have to store a single frame at a time like a 1920 * 1080p which comes out to be a frame size of 5.93MB ( 1920 * 1080 * 24 bits).
Usually you cannot just have 24bit frame buffer in memory the remaining 8bits are padded or have 8 alpha bits.
With HDR the framebuffer depth is usually 64bits (16bit for each component.)
Zbuffer is either 24 or 32bits and if it's 24bits there is 8bits of stencil as well.
If you use MSAA/SSAA you multiply the size of all these buffers by amount of samples 2x, 4x, 8x.
Then you have all vertexes/objects you need to use in the scene and all the textures.
Then you have all special buffers for shadow mapping etc, which can be several 2048x2048x32 buffers.. and so on.
If games uses Deferred rendering you must store all information you need for G-Buffer. (color/albedo, specular, normal, etc.)
If theres GPU side physics and special effects all must reside in there as well.
So yes, there is a proper reasons for more memory.