Typical Scenarios for DMA
System-memory-to-video-memory transfers that use the SRCCOPY raster operation are the most common type of hardware-supported blit operation. (The SRCCOPY raster operation, which is documented in the Windows SDK, causes the data within the source rectangle to be copied directly to the destination rectangle.)
The most typical use for such an operation is to move textures from a large collection of system memory surfaces to a surface in video memory in preparation for subsequent operations.
System-to-video DMA transfers are about as fast as processor-controlled transfers (for example, HEL blits), but are of great utility because they can operate in parallel with the host processor.
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