When the computer-based simulation market emerged 10 to 15 years ago, it came in three forms: strategy war gaming, design and training. Each had its own feature suite, user constituency and vendors. Strategy war gaming was played by groups, usually drawn from senior management, with the goal of exploring strategies for dealing with market conditions. Design simulations optimized the development of new products or enterprise processes. Training simulations educated new personnel about existing devices or environments (a flight simulator to train airline pilots, for instance).The applications did have one thing in common: They all ran on the margins of the enterprise?with a small number of users?for short periods of time set aside for the purpose. They were gamelike, constructed versions of reality. Everyone understood the difference between real experience and simulations. "When experience is lacking, simulation can often take its place," we wrote in our first big piece on the subject ("Some Simulating Experiences," Nov. 1, 1993).The years since 1993 have changed the picture in several ways. The various categories of the simulation technology, for instance, have begun to merge. Once a design simulator improves past a certain level of sophistication, for example, it almost automatically becomes a useful training instrument as well.Ossining, N.Y.-based RSoft produces simulators that support the design of photonic devices and circuits. (Their tools keep track of the underlying physics to see if the design makes sense.) According to company President LuAnn Scarmozzino, until the mid-1990s both universities and optical design companies tended to write their own modeling software. As software makers like RSoft kept adding materials, device definitions, and more elaborate examples and prototypes, however, their programs started to appear in educational contexts. Scarmozzino says that she often sees design simulators being used to retrain engineering talent, thereby allowing skilled personnel to transfer from design fields that are cooling down to ones that the enterprise is more excited about.At the same time, the concept of optimi-zation has spread from designing individual parts (where engineers may try to create maximum strength with minimal material) or processes (to keep maintenance costs on an assembly line at their lowest, for instance) to managing enterprises as a whole. That shift is made possible in part by the growing practice of equipping the elements of enterprises with sensors and network connections. (According to ARC Advisory Group, an automation consultancy in Dedham, Mass., by the end of the decade almost all physical control elements such as motors, switches and valves will be smart in this sense.)The data generated by this "enterprise nervous system" lets managers continuously optimize routine operations such as maintenance cycles. "These days a simulator has to be seen as an integral part of the plant," says Tim Bradley, director of dynamic simulation solutions at Cambridge, Mass.-based AspenTech, a vendor of integrated solutions for process industries. Bradley points out that with sufficient processing power, such simulations can run faster than real-time, giving managers a way to look into the future and see when problems?or opportunities?might emerge in time to do something about them.These trends are running in parallel with another. As product lines turn over more quickly and technologies grow more complex, training is shifting from an episodic activity that happens only during special times (before stepping into a new position, for instance) and locations (classrooms) to one that is continuous, constant and accessible on demand both in time and place. "Increasingly, training is being integrated into and generated by the enterprise knowledge management system itself," observes Nettie Longietti, a project manager at VisionCor, a knowledge management company in Charlotte, N.C.How fast these shifts develop depends in part on how much of enterprise life companies can incorporate into a single dynamic data model. That, in turn, depends on whether HR, marketing, finance and other departments?not only within a single company but also up and down the value chain?are willing and able to hammer out a common set of terms. For the moment, such cooperation is limited at best. (For instance, Scarmozzino would like her simulators to be able to read specifications data directly from supplier or vendor databases, a liberty that manufacturers in her sector do not currently permit.)Nonetheless, for all the hurdles, there is a general expectation that simulations are moving from the edges of the work experience to the heart of it. AspenTech\u2019s Bradley says that he expects managers in charge of constructing new facilities will soon run plant simulations first, and then let the steel-and-brick expression of that simulation follow as an afterthought. Should that happen, reality and metaphor would change places: The simulation would become the real thing.