Kernel space: Memory management for graphics processors
The management of video hardware has long been an area of weakness in the Linux system (and free operating systems in general). The X Window System tends to get a lot of the blame for problems in this area, but the truth of the matter is that the problems are more widespread and the kernel has never made it easy for X to do this job properly. Graphics processors (GPUs) have gotten steadily more powerful, to the point that, by some measures, they are the fastest processor on most systems, but kernel support for the programming of GPUs has lagged behind. A lot of work is being done to remedy this situation, though, and an important component of that work has just been put forward for inclusion into the mainline kernel.
Once upon a time, video memory comprised a simple frame buffer from which pixels were sent to the display; it was up to the system's CPU to put useful data into that frame buffer. With contemporary GPUs, the memory situation has gotten more complex; a typical GPU can work with a few different types of memory:
Video RAM (VRAM) is high-speed memory installed directly on the video card. It is usually visible on the system's PCI bus, but that need not be the case. There is likely to be a frame buffer in this memory, but many other kinds of data live there as well.