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FUTURE COMPUTING ENVIRONMENTS FOR MICROSIMULATION MODELING 216 Advantages of Desktop-Based Environments The rapid emergence of desktop graphical user interfaces characterized by icons, windows, integration with mice, and âpoint and shootâ operation signifies a major change in the manner in which users will interact with computers in the future.82 No microanalytic simulation system currently uses such a platform; SPSD/M is written in the C language to run under MS-DOS, and TRIM2 runs in batch mode under OS/MVx operating systems. The use of icon- and window-based graphical user interfaces will substantially improve the productivity of users of simulation systems written to operate on desktop machines in such environments.83 An important aspect of the computing environment generated and supported by microcomputer technology is the synergistic effect of having sufficient numbers of microcomputer programs that can be applied to data sets.84 For example, aggregate tables produced by SPSD/M can be exported easily to spreadsheet, database, and other programs; such outputs from different simulation runs can be combined easily using other tools in the same computing environment. Furthermore, such work is performed in an interactive dedicated mode of operation, so that the turnaround time for the multiple steps required to use a multiplicity 82 Credit for this revolution can be given to Douglas Engelbart of the Stanford Research Institute in the 1960s and to the Alto development group at Xerox's Palo Alto Research Center. Commercialization began with the Xerox Star and a system from Perq (a now-defunct computer firm in Pittsburgh, Pa.) in 1981, but neither effort was successful. Apple's introduction of the Lisa in 1983 paved the way for the Macintosh in 1984, which has embodied the most widespread such interface. Other products that follow the Macintosh's lead include GEM (Digital Research), Windows (Microsoft), Presentation Manager (IBM), and New Wave (Hewlett-Packard). In the UNIX community the development of X-windows by the Massachusetts Institute of Technology, has spread substantially and now provides a popular windowing platform among UNIX installations; others are Open Look (Sun), DEC Windows (Digital Equipment Corp.), and Motif (under development by the Open Software Foundation). 83 In theory the use of graphical user interfaces and desktop systems is independent. It is possible to conceive of such interfaces connecting desktop terminals with mainframe systems. Two factors mitigate against this, however. First, graphical interfaces require a high bandwidth connection to the processor and memory that is generally not achievable in mainframe usage because of the need to use low-speed communication lines between them. Second, mainframe environments are often optimized for batch computing tasks, and it is unlikely that such an investment in graphical interfaces will be made. Even with the number of IBM 360/370/308Ã/43Ã1/3090 systems installed and with a thriving third-party software market existing for 20 years, we know of no product with such an interface. 84 This synergistic effect can also be observed in systems classified as desktop systems but not microcomputers (e.g., UNIX workstations and scientific workstations). However, the widest range of good software develops and survives in the largest markets, which at present are MS-DOS and Macintosh based.