When IRXINIT initializes a new language processor environment, IRXINIT creates a number of control blocks that contain information about the environment. The main control block is the environment block (ENVBLOCK). The environment block contains pointers to:

• The parameter block (PARMBLOCK), which is a control block containing the parameters IRXINIT used to define the environment. The parameter block IRXINIT creates has the same format as the parameters module.
• The user field that was passed on the call to IRXINIT if IRXINIT was explicitly invoked by a user.
• The work block extension, which is a control block that contains information about the REXX exec that is currently running.
• The REXX vector of external entry points, which contains the addresses of the REXX routines TSO/E provides, such as IRXINIT, IRXTERM, REXX programming routines, and replaceable routines. For replaceable routines, the vector contains the addresses of both the system-supplied routines and any user-supplied routines.
• The TSO/E REXX routine that encountered the first error and issued the first error message in the environment.
• The compiler programming table, which identifies compiler runtime processors and corresponding compiler interface routines.