The Burroughs Large Systems Group produced a family of large 48-bit mainframes using stack machine instruction sets with dense syllables. The first machine in the family was the B5000 in 1961. It was optimized for compiling ALGOL 60 programs extremely well, using single-pass compilers. It evolved into the B5500. Subsequent major redesigns include the B6500/B6700 line and its successors, as well as the separate B8500 line. In the 1970s, the Burroughs Corporation was organized into three divisions with very different product line architectures for high-end, mid-range, and entry-level business computer systems. Each division's product line grew from a different concept for how to optimize a computer's instruction set for particular programming languages. "Burroughs Large Systems" referred to all of these large-system product lines together, in contrast to the COBOL-optimized Medium Systems (B2000, B3000, and B4000) or the flexible-architecture Small Systems (B1000). Background Founded in the 1880s, Burroughs was the oldest continuously operating company in computing (Elliott Brothers was founded before Burroughs, but did not make computing devices in the 19th century). By the late 1950s its computing equipment was still limited to electromechanical accounting machines such as the Sensimatic. It had nothing to compete with its traditional rivals IBM and NCR, who had started to produce larger-scale computers, or with recently founded Univac. In 1956, they purchased ElectroData Corporation and rebranded its design as the B205. Burroughs' first internally developed machine, the B5000, was designed in 1961 and Burroughs sought to address its late entry in the market with the strategy of a completely different design based on the most advanced computing ideas available at the time. While the B5000 architecture is dead, it inspired the B6500 (and subsequent B6700 and B7700). Computers using that architecture were still in production as the Unisys ClearPath Libra servers which run an evolved but compatible version of the MCP operating system first introduced with the B6700. The third and largest line, the B8500, had no commercial success. In addition to a proprietary CMOS processor design, Unisys also uses Intel Xeon processors and runs MCP, Microsoft Windows and Linux operating systems on their Libra servers; the use of custom chips was gradually eliminated, and by 2018 the Libra servers had been strictly commodity Intel for some years. B5000 The first member of the first series, the B5000, was designed beginning in 1961 by a team under the leadership of Robert (Bob) Barton. It had