Any memory over and
above the memory used for the framebuffer may be used for fonts, off-screen
rendering, save-unders (remembering what is underneath windows), and texture
maps.
Graphics processing unit (GPU)
Performs graphics operations such as block moves, line drawing, area fills, shading,
and texture mapping independently from the system??™s CPU. Most modern
GPUs handle 3D operations, although some of the lower-end devices (typically
built into motherboards) have very weak 3D performance.
Bus interface
Connects the host system bus to the memory and GPU. PCI Express (PCI-E) is
the preferred connection path on most new systems; an accelerated graphics port
(AGP) or legacy PCI interface may also be used.
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18 Chapter 1: Introduction to the X Window System
Video controller
Generates the video signal by repeatedly scanning the framebuffer and converting
the pixel information into the format required at the video connector. If an
analog connection is used, multiple digital-to-analog converters (DACs) are
incorporated to convert the digital brightness values into varying voltages; the
DACs speed often limits the maximum refresh rate available at a given resolution.
Some graphics systems with DVI, HDMI, or DisplayPort connectors incorporate
encryption chips between the video controller and the video connector.
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