A single user operating system is a system in which only one user can access the computer system at a time. On the other hand, a multi-user operating system more than one user to access a computer system at one time.
A single user operating system provides the facilities to be used one computer by only one user. In other words, it supports one user at a time. However, it may support more than one profile. Single keyboard and single monitor are used for the purpose of interaction. Most of the home and office PCs are the single-user system.
On the other hand, a multiuser operating system is designed for more than one user to access the computer at one time. Generally, one a network environment, a computer can be remotely used. Mainframes and server computers are examples who work in a multiuser environment. The operating systems with multiuser support are more complex in comparison to single-user operating systems.