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# Portability

Today, the half-life of computer technology is approximately two to three years. To realize proper longevity of the modeling software, it needs to be written in a portable language to allow the software to be moved readily from processor to processor without requiring the modeling software or users to change. Then, when it is desirable to take advantage of the constantly increasing processor capabilities and similarly increasing memory capacity by replacing the installed hardware base, there are a minimum of ancillary costs. Also, it may be desirable to connect together processors from a variety of vendors, with the workload judiciously allocated to the types of hardware that best support the requirements of each particular application program. This distribution of processing when coupled with the fact that users are spread out over multiple locations makes networking a vital ingredient as well.

BRL's strategy for achieving this high level of portability was to target all the software for the UNIX operating system, [RT78], with all the software written in the ``C'' programming language [RJLK78]. The entire BRL-CAD Package, including the MGED editor is currently running on all UNIX machines at BRL, under several versions of the UNIX operating system, including Berkeley 4.3 BSD UNIX, Berkeley 4.2 BSD UNIX, and AT&TSystem V UNIX.

The list of manufacturers and models of CPUs that support the UNIX operating system [Dei84] is much too lengthy to include here. However, BRL has experience using this software on DEC VAX 11/750, 11/780, 11/785 processors, Gould PN6000 and PN9000 processors, Alliant FX/8 and FX/80 processors (including systems with eight CPUs), Silicon Graphics IRIS 2400, 2400 Turbo, 3030, 4-D, and 4-D/GT workstations, the Cray X-MP, the Cray-2, and the ill-fated Denelcor HEP H-1000 parallel supercomputer.