äBatch multiprogramming does not support interaction with users äTSS extends multiprogramming to handle multiple interactive jobs äMultiple users simultaneously access the system through terminals äBecause of slow human reaction time, a typical user needs 2 sec of processing time per minute äThen (about) 30 users should be able to share the same system without noticeable delay in the computer reaction time äThe file system must be protected (multiple  users…)