Each operating system acquires a unique set of characteristics reflecting the needs of its users. The basic distinction among ESL9322SL Tape Library 11 operating systems is the - processing method each system uses to execute tasks. The selection of an oper- ating system will reflect the following processing options • Single-user ESL9322SL Tape Library vs. multiuser • Single-job vs. foreground/background • Foreground/background vs. multiprogramming • Timesharing vs. event-driven multiprogramming • Realtime ESL9322SL Tape Library Single-user systems do not require account numbers to access the system or data files. Nor do these systems usually provide protection for user programs. RT 11 is a single-user operating system. - A multiuser ESL9322SL Tape Library operating system receives demands for its resources from more than one individual and/or program. The system must manage its resources based on these demands. For example, several users may want sole control of a device at the same time. The system handles access to the device. In ESL9322SL Tape Library addition, because people may be using the system for different purposes, privacy must be an option. As a result, a multiuser system normally has an account system to manage different users' files. The ESL9322SL Tape Library/E, Micro/RSTS, ULTRIX- 11, DSM-11, RSX-11M, RSX-11M-PLUS, and Micro/RSX systems are multiuser systems. It is ESL9322SL Tape Library important to consider what operating system(s) are required to use the desired applications. The ESL9322SL Tape Library operating systems that run on PDP 11s offer process- - ing environments. These systems are described in the following section.