Microsoft Windows was first announced at the Fall COMDEX 1983 computer expo as a cooperative multitasking desktop environment with a tiling window manager. Contrary to popular belief, the tiling was not a design nor legal limitation, but rather a conscious choice for main application windows backed by research at Xerox PARC, where some members of the Windows team had previously worked at. Windows did indeed fully support overlapping windows, though in practice the ability was originally only used for popup windows and certain controls such as menus and dropdowns. Although Windows ended up supporting MS-DOS hosts only until the introduction of Windows NT, Microsoft also considered porting Windows to Xenix as well as the multitasking MS-DOS 4. However, ultimately neither port ended up materializing.