vid_nopageflip
This variable toggles the use of page-flipping during supported video modes. By default the game will allow for page-flipping for video modes that support this feature. For example if a given VESA mode can support page flipping, then it defaults to page-flipped operation. A VESA mode can be forced to non-page-flipped operation by setting the "vid_nopageflip" variable to "1", then setting the mode (note that "vid_nopageflip" takes operation on the next, not the current video mode, and note that it then stays in effect permanently, even when the client is exited and restarted, unless it is manually set back to "0"). If there is not enough memory for two pages in a VESA mode, or if the adapter doesn't support page flipping, then the mode will automatically be non-page-flipped. Page-flipping works by drawing multiple virtual game screens at the same time in the video memory and then switching among them to display the current gamescreen. Page-flipped modes thus use less system memory than non-page-flipped modes, but require more video memory. When using page-flipping, visual quality may be higher, but performance of the game can change to better or worse, depending on the graphics adapter and other hardware (see the discussion of the Pentium Pro below, for a discussion of why page flipping can be faster but is sometimes much slower on that processor). However in most cases the performance (and thus frame rate) will be increased, but for people with hardware that has problems with page-flipping "vid_nopageflip 1" may help. The Pentium Pro is an example for such a hardware: it is an okay client platform (sniff!), but it has one weak spot, it is by default very slow on writes to video memory. This means that in default hardware configurations, you are usually much better off setting "vid_nopageflip" to "1" if you use VESA modes, so drawing is done to system memory instead of to video memory. Remember that you must set the mode after setting "vid_nopageflip" to "1" in order to get "vid_nopageflip" to take effect. "vid_nopageflip 1" can sometimes be faster on a Pentium too, but not by nearly as much in general, and it's often slower.