What is a RES File Type?
With the release of Half-Life, which was Valve Software's first title, the RES files became dominant in 1998. The files were used to store the location of resources instead of the resources themselves to reduce download time. During a game like Half-Life, the file RES is referenced by the game if the player plays a personalized card then downloads the resources, making them playable in the game.
As download speeds have increased, new resource formats have been released, and the game engine has evolved, real RES files have become less common. RES files are now generally integrated into the map files with which they are associated, using BSPZIP, an-line command tool. If, however, a map with built-in resource lists cannot be accepted, the RES file can be used.
If the BSP is loaded by the game, it is probably because of apos; a typo in one or several paths of resources. To view and edit the RES file, you can use a text editor.
In order to be recognized by a game, a RES file must be placed in the \maps folder along with the BSP card, which accompanies and also bears the same name as the BSP card.