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FUTURE COMPUTING ENVIRONMENTS FOR MICROSIMULATION MODELING 204 MB with respectable access and transfer rates is not uncommon now. On a dedicated basis, the capacities and speeds of current devices perform as well or better than their mainframe counterparts do on a shared basis. For sequential low-cost storage, classical nine-track half-inch magnetic tape drives with moderate performance characteristics have been available for microcomputers for some time, but relatively high costs and somewhat bulky equipment have discouraged widespread use. A much more promising arrival is digital audio tape (DAT), which is expected to become considerably cheaper, substantially more capacious, smaller, and sufficiently fast for microcomputer-based large file operations.57 In 1989â1990, 1-gigabyte (109 or 1,000,000,000 bytes) DAT devices capable of operating as directory devices using block recording techniques are expected to become available. In addition, the erasable optical disk, first introduced in a desktop product in fall 1988,58 is now becoming more common, and larger capacities and faster access times are appearing. Such devices are likely to become standard in microcomputer environments for large file storage as well as routine file backup and restore operations. These devices are likely to become the microcomputer equivalent of magnetic tape in the near future. Advances in Software Methodology The history of electronic computing has been characterized by hardware developments leading software developments. Characteristically, the hardware available has exceeded our ability to exploit it fully. As the price of hardware has decreased substantially, appropriate use has replaced maximal use as a relevant issue. Nevertheless, the art of constructing programs and software systemsâsoftware engineeringâremains very important in terms of extracting value from computing hardware. Two recent developments in software engineering are worth noting in 57 Digital audio tape (DAT) technology for storing computer data is based on the development of DAT technology for sound reproduction, which at the time of this writing (1989) is emerging as a technology for storing digitized music and other sound on very small cassettes using a recording technology based on digital helical recording techniques. Application of DAT technology to computer use benefits substantially from the use of the product in the consumer audio market, much the same as development of CD-ROM (compact disk-read only memory) products for microcomputers was derived from the development of the consumer compact disk audio market. The economies of scale of production for the consumer audio market result in lower prices for computer-related products that utilize these technologies. 58 The NeXT computer system, announced in October 1988, contains a 256-MB erasable optical disk. Approximately a year later, a number of companies were selling add-on-erasable optical disk drives for MS-DOS and Macintosh systems with a capacity of 300 MB per side. A 3.5-inch form factor erasable optical disk is being developed by at least one manufacturer; such disks have a capacity of 150 MB.