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<A HREF="ati.html"><EM>ATI Adapters README file</EM></A>
 <b>:</b> <EM>A note on acceleration</EM><BR>
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  <H2><A NAME="2"></A>2. A note on acceleration</H2>
<p>The meaning of "acceleration", as used in this document, needs to be clarified.
Two of the many components in an accelerator are the CRT controller (CRTC) and
the Draw Engine.
This is in addition to another CRTC that, generally, is also present in the
system (often in the same chip) and typically provides EGA, VGA or SuperVGA
functionality.</p>
<p>A CRTC is the component of a graphics controller that is responsible for
reading video memory for output to the screen.
A Draw Engine is an accelerator component that can be programmed to manipulate
video memory contents, thus freeing the CPU for other tasks.</p>
<p>When the VGA CRTC is used, all drawing operations into video memory are the
responsibility of the system's CPU, i.e. no Draw Engine can be used.
On the other hand, if the accelerator's CRTC is chosen to drive the screen,
the Draw Engine can also be used for drawing operations, although the CPU can
still be used for this purpose if it can access the accelerator's video
memory.</p>
<p>Video acceleration refers to the programming of an accelerator's Draw Engine to
offload drawing operations from the CPU, and thus also implies the use of the
accelerator's CRTC.</p>

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<A HREF="ati.html"><EM>ATI Adapters README file</EM></A>
 <b>:</b> <EM>A note on acceleration</EM><BR>
<b>Previous:</b> <A HREF="ati1.html"><EM>Statement of intent</EM></A><BR>
<b>Next:</b> <A HREF="ati3.html"><EM>Current implementation for ATI adapters</EM></A>



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