System services are prewritten system routines that perform a variety of tasks, such as controlling processes, communicating among processes, and coordinating I/O.
Unlike the OpenVMS Run-Time Library (RTL) routines, which are divided into groups by facility, all system services share the same facility prefix (SYS$). However, these services are logically divided into groups that perform similar tasks. Table 3-11 describes these groups.
| Group | Types of Tasks Performed |
|---|---|
| AST | Allows processes to control the handling of asynchronous system traps (ASTs). |
| Change mode | Changes the access mode of particular routines. |
| Condition handling | Designates condition handlers for special purposes. |
| Event flag | Clears, sets, reads, and waits for event flags, and associates with event flag clusters. |
| Information | Returns information about the system, queues, jobs, processes, locks, and devices. |
| Input/Output | Performs I/O directly without going through RMS. |
| Lock management | Enables processes to coordinate access to shareable system resources. |
| Logical names | Provides methods of accessing and maintaining pairs of character-string logical names and equivalence names. |
| Memory management | Increases or decreases available virtual memory, controls paging and swapping, and creates and accesses shareable files of code or data. |
| Process control | Creates, deletes, and controls execution of processes. |
| Security | Enhances the security of OpenVMS systems. |
| Time and Timing | Schedules events and obtains and formats binary time values. |