Why is the Windows taskbar default at the bottom?

In Windows operating systems the taskbars default position is at the bottom. Why is that so? Especially it is strange to me because all windows application have their main menu bar at the top. To me it makes more sense to have the main operating systemu menu (which the taskbar is) at the top where all other program have their main operating menu, where they are controlled from. Web browsers with tabbed interfaces also have tabs at the top, not the bottom.