Now that it is gone, I can talk about it.
Windows NT4 server came out in 1996 and replaced our novell netware server. actually Nt server 3.51 replaced the netware but then we upgraded it.

Well.. it’s been running ever since acting as a Primary Domain Controller and was just shut down this past week. The hardware that it had to run on was almost just as old.. circa 2001-2003.
It was very finicky in that it could not see a partition bigger than 4gb on its boot drive.
None of the firewalls would work with it. It was a dangerous legacy that was replaced with a modern OS, linux fedora 20 with samba4. the hardware is still pretty old but is reliable.

So far so good, no one has noticed the replacement, in terms of broken or reduced functionality.