You have initiated an active operating system fingerprinting attempt with nmap against a target system: What operating system is the target host running based on the open ports shown above?

Windows XP presents a different nmap OS fingerprint - it shares some ports but its TCP/IP stack parameters (window size, IP ID sequences) differ enough that nmap distinguishes it from Windows 2000 Server.

Windows 98 SE lacks native SMB over TCP/IP (port 445), does not run server-grade RPC services on port 135, and presents a fundamentally different lightweight port profile that nmap would not match to a server OS.

Windows NT4 Server predates SMB over port 445 and presents older TCP/IP stack characteristics with a different fingerprint pattern that nmap's database distinguishes from Windows 2000.

Windows 2000 Server exposes a distinctive combination of open ports including 135 (RPC endpoint mapper), 139 (NetBIOS Session Service), and 445 (SMB over TCP), along with specific TCP/IP stack behaviors such as TTL values and window sizes that nmap matches against its OS fingerprint database. Nmap's active fingerprinting sends tailored probes and compares responses to its database, uniquely identifying Windows 2000 Server versus other Windows versions.