Simultaneous Users: Lets say that users are logging into application, send a mail and logout. In this process, every user will wait for the other user to complete the entire transaction before logging. here at any point in the scenarion no 2 users are logged in to the system. simple words one after the other.
Concurrent Users: There are 3 different levels of concurrency.
1. Application level
2. Business process level
3. Transaction level
Taking the above example
- Application level : two users login but one user can send a mail and other can read a mail. Notice 2 users although active at the system at the same time, they perform 2 diffferent processes.
- Business process level: two users login to the system and send mails. But they dont login at the same time and send mails. It can so haapen that one user is coposing amil, 2 nd user logs in. first users sending a mail, second user composing. ...and so on..Point to notice here is 2 u sers are active on the system doing the same busineess process but niot all actions at a time.
- Transactin level: 2 users login at teh same time, compose at the same tiem and sends mail at the same time and logs out at teh same time. (Randezvous).
Overall when we say 10 concurrent users, 10 users are currently active on the system at that point of time. When we say 10 simultaneous users which is not the case.