Which one of the following is not a multi-user operating system ?

Which one of the following is not a multi-user operating system ?

UNIX
Windows XP
MS-DOS
Windows 2000
This question was previously asked in
UPSC CISF-AC-EXE – 2023
MS-DOS (Microsoft Disk Operating System) is a single-user, single-tasking operating system. This means it was designed to be used by one person at a time and could run only one program at a time.
– Multi-user operating systems allow multiple users to access and use the system concurrently.
– UNIX, Windows 2000, and even later versions like Windows XP (though primarily desktop OS, they have features like Fast User Switching and support for services running under different users, and Windows 2000 was a significant multi-user capable OS designed for servers/workstations) are capable of multi-user operation to varying extents.
– MS-DOS strictly lacks multi-user capabilities.
Modern operating systems like Windows (NT-based versions onwards), macOS, and Linux/UNIX are inherently multi-user, although their implementation and typical usage scenarios differ (e.g., desktop vs. server).