20.4.2 System Service Routines
  System services are 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 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 20-3 describes these groups.