Microsoft had gone through its own round of operating system development. Initially, they partnered with IBM to develop an Intel-based disk operating system called PC DOS, and its Microsoft twin, MS-DOS. Eventually, Microsoft shared true network operating system development with IBM LAN Manager and its Microsoft twin, Microsoft LAN Manager. Microsoft parted company with IBM and continued developing LAN Manager into what became Windows NT. Essentially, its OS 4.0. NT was originally a flat server or domain-based operating system with none of the advantages of VINES or NDS.