In the period surrounding Win2K, the user level Windows versions were all "DOS based." The DOS-based systems were good enough for individual users' computers, but in the time when Win2K appeared they had limited ability to "network" even at user group levels, and connecting to a real network generally required use of separate "interface programs" that seldom worked as expected. (voice of limited experience)

The introduction of Windows NT, partly to provide a more "network capable" operating system, was less than successful, with the biggest problem possibly being that few people could really decide whether the additional things it could do were worth the additional user effort required to make it do them.

Win2K was a significant redesign based deliberately "more on NT than on DOS," although I don't recall whether the starting point was NT2 or NT3. The intent was to provide a PC (personal computer) operating system with decent built-in compatibility with the network server systems in use at the time.

During its lifetime, Win2K was probably more "secure" than co-existing "PC Windows" versions, required far fewer security patches, and was very much more "stable" than other versions extant at the same time. It almost never crashed (unless one tried to do something for which it wasn't really intended, or did something incorrectly) and it earned the reputation among network administrators for being much easier to "manage."

It's now old and tired, and should be put to rest by most users, although it did maintain a longer period of actual viability than several "lesser" Windows versions that appeared and faded during its life span.

John