Three ways that multi user OS provide protected environments
are
Through Account Seperation : This means that the different
users accessing the system have their own accounts and with that
comes their own storage space isolated from one other which
prevents accidently deleting other person's work.
By Assigning Roles and Permissions : Each user accessing the
system will be given a defined set of permissions within which only
he can do the work.
Protecting each persons work with the use of a secure
encryption which is unique to the particular user.Accidently or
purposefully if some one tries to access the work of others then
that user must be authenticated to access the particular
resource.