VIRTUAL DATA

In the 1970s, when computers were memory limited, operating system des igners created the concept of ''virtual memory'', which gave users the ability to address more memory than physically existed. In the 1990s, many large control systems have the potential of becoming data limite d. We propose that many of the principles behind virtual memory system s (working sets, locality, caching and clustering) can also be applied to data-limited systems, creating, in effect, ''virtual data systems' '. At the Los Alamos National Laboratory's Clinton P. Anderson Meson P hysics Facility (LAMPF), we have applied these principles to a moderat ely sized (10000 data points) data acquisition and control system. To test the principles, we measured the system's performance during tune- up, production, and maintenance periods. In this paper, we present a g eneral discussion of the principles of a virtual data system along wit h some discussion of our own implementation and the results of our per formance measurements.