Explain the difference between multiuser and multitasking. Give an example of an OS that is multiuser and one that is not.?

The X25 demodulator machine has been upgraded to modern computer architecture standards. Additionally , the X25 OS supports pre emptive multitasking and one to one relationship between user level threads and kernel level threads which allows one or more threads from a process to issue blocking system calls while other threads(within that process) continue to run. Explain with design detail how the X25 kernel may provide for a user level thread implementation?