The GT.M data management system consists of a run-time library and a set of utilities which operate on one or more user-specified Global Directories (GD) and database files. GT.M stores M global variables in database files. Internally, the database files are organized as balanced trees (B-trees) in Greystone Data Structures (GDS). For more information on B-trees and the GDS file structure, refer to the "Greystone Database Structure" chapter.

A Global Directory organizes global variables and specifies the initial operation characteristics for a newly created database. The Global Directory maps global names to a database file, then GT.M uses this mapping when storing and retrieving globals from the database. Multiple Global Directories can reference a single database file, except when database replication is in use. Use the Global Directory Editor (GDE) to create a Global Directory.

After defining the specifications in the Global Directory, use the CREATE command from the M Peripheral Interchange Program (MUPIP) to create database files.

GT.M uses logical names to locate the Global Directory or database files. This permits selection of appropriate physical database files at run time, without the need to modify the M application.