Graphics resources that are allocated from system memory with write-back caching will utilize the full cache hierarchy: Level 1 (L1), Level 2 (L2), last-level cache (LLC), optional EDRAM, and finally DRAM. When accessed from the GPU, sharing can occur in LLC and further caches/memory. The Intel® Processor Graphics Gen9 GPU has numerous bandwidth improvements including increased LLC and ring bandwidth. Coupled with support for DDR4 RAM, these help hide latency.
When detecting the amount of available video memory for your graphics device, remember that different rules may apply to different devices. An integrated graphics part reports only a small amount of dedicated video memory. Because the graphics hardware uses a portion of system memory, the reported system memory is a better indication of what your game may use. This should be taken into account when using the reported memory as guidance for enabling or disabling certain features. The GPU Detect Sample shows how to obtain this information in Windows*.