Query with window XP

I have window XP operating system and I happen to see a exe called as rundll32.exe.Is this same as rundll.exe present in other versions of windows namely windows9x.If not what is the difference between the two . Also could someone tell me the usage of the exe namely rundll32.exe.

Rundll32.exe is the program which loads and manages dll library files in windows XP. Rundll.exe do the same work in windows previous versions. But if you see one rundll.exe in windows XP, it might be a virus or trojan!!