A mechanism for exchanging program segments while a program is running

To allow continuous computer operation without down time, a mechanism is proposed for exchanging parts of a program while it is being executed as a process. First, the program conditions and process conditions are listed that are essential for such an exchange. The program conditions are related to the function interface, program flow and external addresses, and the process conditions are related to the process execution state. Second, flags are introduced to indicate the relation between the program and processes that are using the program. These flags are used to determine the program and process conditions and to control process execution during exchange of program segments. Finally, some implementations of this mechanism are described as well as some functions given by the operating system. Algorithms are explained and a trial model is evaluated. The results show that software maintenance can be carried out while a computer is in operation with little degradation of service.