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.
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.
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.
Most 1MB cards cannot display modes larger than 1024x768 with a decent refresh rate, leaving 256kb unused.
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