A persistent system in real use-experiences of the first 13 years

Eumel and its advanced successor L3 are operating systems built by GMD which have been used, for 13 years and 4 years respectively, as production systems in business and education. More than 2000 Eumel systems and 500 L3 systems have been shipped since 1979 and 1988. Both systems rely heavily on the paradigm of persistence (including fault-surviving persistence). Both data and processes, in principle all objects are persistent, files are implemented by means of persistent objects (not vice versa) etc. In addition to the principles and mechanisms of Eumel/L3, general and specific experiences are described: these relate to the design, implementation and maintenance of the systems over the last 13 years. For general purpose timesharing systems the idea is powerful and elegant, it can be efficiently implemented, but making a system really usable is hard work