This is the none compiled version of the models, (geometry, UVs coords, skeleton, and animations)

SMD file are ascii file, it mean that you can open them in a text editor all data a readable for a human.

SMD files must to be compiled into binary format (*.MDL), with the help of the QC Script, studioMDL.exe .

MDL file format is the format file that is compatible with the valve source Engine.