For best results, if you're running a busy production server, you should place TempDB on a seperate drive and split it up into one file for each CPU. That way, each scheduler has its own TempDB file to work with, which can greatly speed things up when running parallel operations (a disk will always be slow compared to a CPU, but at least if they're not all constantly asking for the same file...;-)) All TempDB files should be equally sized and have the same autogrowth settings.