Freeze could also be in three forms – temporary, permanent and controlled. Temporary meant that once the client count dropped to zero, the library would be unfrozen and terminated. Permanent meant that the library remained available for further clients even if the client count dropped to zero – permanent libraries could be unfrozen by an operator with a THAW command. A controlled freeze meant that the library actually kept running, so that it could execute monitoring functions and perform data initialization and cleanup functions for each linking client.