B5000

In the 1970s, 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. The Burroughs Large Systems Group designed large mainframes using stack machine instruction sets with dense syllables and 48-bit data words. The first such design was the B5000 in 1961. It was optimized for running ALGOL 60 extremely well, using simple compilers. It evolved into the B5500. Subsequent major redesigns include the B6500/B6700 line and its successors, and the separate B8500 line. 'Burroughs Large Systems' referred to all of these product lines together, in contrast to the COBOL-optimized Medium Systems (B2000, B3000, B4000) or the flexible-architecture Small Systems (B1000).

Founded in the 1880s, Burroughs was the oldest continuously operating entity in computing, but by the late 1950s its computing equipment was still limited to electromechanical accounting machines such as the Sensimatic; as such 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. While in 1956 it branded as the B205 a machine produced by a company it bought, its 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 & B7700). Computers using that architecture are 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.

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