<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<TITLE>Acceleration issues </TITLE>
</HEAD>
<BODY BGCOLOR="#efefef" TEXT="black" LINK="blue" VLINK="#551A8B" ALINK="red">

<A HREF="tseng.html"><EM> Information for Tseng Chipset Users</EM></A>
 <b>:</b> <EM>Acceleration issues </EM><BR>
<b>Previous:</b> <A HREF="tseng10.html"><EM>Mode issues </EM></A><BR>
<b>Next:</b> <A HREF="tseng12.html"><EM>ET6000 memory size facts and fiction </EM></A>


<HR NOSHADE>
  <H2><A NAME="18"></A>11. Acceleration issues </H2>

<p>The XFree Acceleration Architecture makes extensive use of the unused video
memory on the VGA card. If there is not enough free video memory, some
acceleration features will be disabled or crippled, resulting in less
performance.</p>
<p>To avoid this from happening, try to keep an absolute minimum of 16 kb of
free memory, in addition to the 1kb already reserved by the accelerator.</p>
<p>In practice, this small amount of memory should not be a problem. Most cards
nowadays have 2 MB of video memory, and running 1280x1024 still leaves
plenty of memory unused. Even a 1600x1200 desktop will leave over 170kb
unused, which will then be used by the accelerator to enhance performance.</p>
<p>Most 1MB cards cannot display modes larger than 1024x768 with a decent
refresh rate, leaving 256kb unused.</p>
<p>The order in which free memory is used to accelerate certain features is as
follows.</p>
<p>If no video memory is unused (i.e. all of it is used for display memory),
no acceleration can be used at all -- not even a hardware cursor on the
ET6000.</p>
<p>If the hardware cursor is enabled (ET6000 only) and there's at least 1kb of
free video memory, 1kb is used for that.</p>
<p>If there is at least 1kb of free memory remaining after this, most
acceleration features are enabled as well, reserving an extra 1kb of video
memory.</p>
<p>If there's still some free memory, some extra acceleration features are
enabled. These require more free video memory, depending on the virtual
screen width and the color depth (bpp). The server will print out how much
memory it used if it could.</p>
<p>If there's still some free video memory, it is used as a pixmap cache. This
way, small patterns and images can be kept in the video memory so that they
don't need to be transferred into the video memory each time they're needed.
This is beneficial because transferring an image over the bus to the video
memory takes a lot more time than letting the accelerator blit it from the
pixmap cache to the display memory.</p>

 <HR NOSHADE>
<A HREF="tseng.html"><EM> Information for Tseng Chipset Users</EM></A>
 <b>:</b> <EM>Acceleration issues </EM><BR>
<b>Previous:</b> <A HREF="tseng10.html"><EM>Mode issues </EM></A><BR>
<b>Next:</b> <A HREF="tseng12.html"><EM>ET6000 memory size facts and fiction </EM></A>



</BODY>
</HTML>
