The blackboard model is both simple to understand and, in our case, simple to construct. The paradigm is that of a number of independent players with pieces of a jigsaw puzzle. One player might put a piece on the blackboard, and others will attempt to fit their pieces into the puzzle as connections become apparent. All the information necessary to complete the puzzle is posted on the blackboard, and seen by all players simultaneously. Additionally, the solution is achieved by independent players who need not communicate with each other, except through the blackboard.
All processes can see the status of all observations at the same time.
When complete, it reposts the revised status of that observation, and continues its search for something to do. But each of these solutions again requires a controller specifically to guard against the ambiguities of concurrency. File systems constitute one of the central parts of any operating system, and have received a great deal of attention in their design to problems of concurrency. Especially in environments where multiple machines are clustered with common access to files on multiple devices, the operating system is required to deal explicitly with lockouts, exclusions, and race conditions. By using the file system we avoid duplicating a fairly complete, complex, and sophisticated piece of software with a proven ability to deal with concurrency problems.