Overview

THE OPENVMS ENVIRONMENT in which DCL commands are executed and programs are run is called the process. A process provides the structure and information necessary to run the program images that make up DCL, OpenVMS utilities, and application software. A component of OpenVMS called the scheduler is responsible for periodically choosing a process to run on each VAX or Alpha processor. The scheduler must ensure that all processes get their fair share of the VAX or Alpha execution cycles. The following components are associated with every OpenVMS process:

• A set of data structures containing control information for the process. These structures are maintained by OpenVMS in an area of system memory called S0 space. Some of the control information is described in the next section.

• A private area of virtual memory called P0 space. A program image invoked with the RUN command or directly with its own command (e.g., PHONE) is executed in P0 space.

• A private area of virtual memory called P1 space. When a process is being controlled by the DCL command interpreter, the DCL program image is located and running in P1 space. Symbols and process logical names are maintained in P1 space. Information about executing command procedures, as well as temporary stack storage for images, is also maintained in P1 space.

OpenVMS supports various kinds of processes, five of which you are likely to encounter in your adventures with OpenVMS:

Interactive An interactive process is created...