Graphics Accelerators
As the demand for better graphics increased, hardware manufacturers created a way to decrease the amount of CPU time required to fill the framebuffer. This is commonly called a "graphics accelerator" in the Unix world.
Common graphics drawing commands (many of them geometric) are sent to the graphics accelerator in their raw form. The accelerator then rasterizes the results of the command to the framebuffer. This method can save from thousands to millions of CPU cycles per command, as the CPU is freed to do other work.
While early accelerators focused on improving the performance of 2D GUI systems, most modern accelerators focus on producing 3D imagery in real time. A common design is to send commands to the graphics accelerator using a library such as OpenGL. The OpenGL driver then translates those commands to instructions for the accelerator's graphics processing unit (GPU). The GPU uses those microinstructions to compute the rasterized results. Those results are bit blitted to the framebuffer. The framebuffer's signal is then produced in combination with built-in video overlay devices (usually used to produce the mouse cursor without modifying the framebuffer's data) and any analog special effects that are produced by modifying the output signal. An example of such analog modification was the spatial anti-aliasing technique used by the 3dfx Voodoo cards. These cards add a slight blur to output signal that makes aliasing of the rasterized graphics much less obvious.
At one time there were many manufacturers of graphics accelerators, including: 3dfx; ATI; Hercules; Trident; Nvidia; Radius; S3 Graphics; SiS and Silicon Graphics. The market is currently dominated by just two companies, Nvidia (incorporating 3dfx from 2002) and AMD (who purchased ATI in 2006).
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