Most batch processing systems for mainframe computers may also be considered "multi-user", to avoid leaving the CPU idle while it waits for I/O operations to complete.
Similar functions were also available in a variety of non-Unix-like operating systems, such as Multics, VM/CMS, OpenVMS, MP/M, Concurrent CP/M, Concurrent DOS, FlexOS, Multiuser DOS, REAL/32, OASIS, THEOS, PC-MOS, TSX-32 and VM/386.
Some multi-user operating systems such as Windows versions from the Windows NT family support simultaneous access by multiple users (for example, via Remote Desktop Connection) as well as the ability for a user to disconnect from a local session while leaving processes running (doing work on their behalf) while another user logs into and uses the system.
Multi-user operating systems such as Unix sometimes have a single user mode or runlevel available for emergency maintenance.
Examples of single-user operating systems include MS-DOS, OS/2 and Classic Mac OS.