Global Directories are files that are central to the operation of GT.M. GT.M provides flexibility in database configuration by allowing each process to distribute its logically monolithic global variable name space across an arbitrary number of database files. This is performed with the aid of a Global Directory file in its working directory, or specified by a environment variable. A Global Directory file maps a region (a range of global variable names) to a segment (a file name or a file specified indirectly ). GT.M utilities and the run-time system for GT.M processes use Global Directories to locate global data.

MUPIP CREATE uses Global Directories to define the specifications for creating database files. A Global Directory file:

Typically, M programs using the same Global Directory share all of the same global variables. However, by using environment variables in file names, the same Global Directory can be used to map global variables to different files for different processes.

For example, two executing images share the same Global Directory file, and direct specified globals into the production database file. This mapping of specified variables is defined by the Global Directory file that is indirectly access through a logical name an environment variable. If there is an operational need, the production processes can be redirected to a different Global Directory file. Executing processes can dynamically change global directories, or force a specific database access to use a specific Global Directory other than its current Global Directory. Two global directories can map segments (either the same or different global variables) to the same database file.