The Accessroutines is a collection of specialized routines that allow many users to access the database concurrently. The Accessroutines is responsible for all physical and logical management of the database.

In a multiprocessing environment, the first program to open the database causes the Accessroutines to be loaded in main memory. Since the Accessroutines is reentrant, all subsequent programs which open the database are automatically attached to the Accessroutines that is currently running. The operating system ensures that only one copy of the Accessroutines is active for each database. This process provides proper control and synchronization when several programs are accessing the database concurrently.