by the Modcomp Classic; the first Classic model was the 7810. This retained compatibility with the Modcomp IV, while offering full support for 32-bit addressing. The later 9250 and 9260 continued to support both 16-bit and 32-bit applications. Operating systems The Modular Applications eXecutive family of operating systems supported these machines. MAX I was a real-time monitor for a fixed set of processes linked into a single memory image. This met the requirements of many embedded systems. MAX II was a batch disk operating system with real-time extensions. It could be used for program development in the background while foreground processes handled real-time loads. These systems used Fixed priority pre-emptive scheduling. MAX III (for the 16-bit machines) and MAX IV (for the Modcomp IV) allowed for multiple interactive users. In MAX III, all processes shared the one address space with swapping used to support multiple background processes, one per interactive user. The MAX IV operating system was largely compatible, while it took advantage of the new features of the Modcomp IV to allocate one address space for each process. Demand paging was not supported, and swapping was used when the total memory demand for all processes exceeded the available physical memory. The operating system also took advantage of the 15 registers to reduce time required to change program environments. The successor to MAX IV, developed to fully exploit the Modcomp Classic system, was called MAX 32. Program Development In addition to a very capable Macro-Assembler, the Fortran system also was designed to take advantage of the multiple registers to temporarily hold the values of variables and indexes. The compiler also had optimization which reduced the number of operations required to process math expression most often found in indexing into arrays. The compiler also produced Macro-Code that when processed by the Macro-Assembler produced loadable machine code. When the Modcomp IV was released, the output of the compiler's code could be modified to take advantage of newer instructions available in the hardware. Applications Many of Modcomp's early sales were for tracking and data collection from NASA space probes, and in the 1980s they provided a network of 250 Modcomp II systems to control the Space Shuttle launch complex at Cape Canaveral as well as SET at SAIL at JSC until T-30, at which point control was handed over to a single IBM mainframe. In the 1990s Modcomp developed a product in the