Burroughs B1700
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The Burroughs B1000 Series machines consisted of three major generations. These were the B1700, B1800, and B1900 series machines.
Much original research for the B1700, initially codenamed the PLP ("Proper Language Processor" or "Program Language Processor") was done at the Burroughs Pasadena plant. ¹
Production of the B1700s began in the mid 1970s and occurred at both the Santa Barbara and Liege, Belgium plants. The majority of design work was done at Santa Barbara with the B1830 being the notable exception designed at Liege.
The B1000 is distinguished from other machines in that it emulated a writeable control store allowing the machine to simulate any other machine. The Burroughs MCP (Master Control Program) would schedule a particular job to run. The MCP would preload the interpreter for what ever language was required. These interpreters presented different virtual machines for Cobol, Fortran, etc.
A notable idea of the "semantic gap" between the ideal expression of the solution to a particular programming problem, and the real physical hardware illustrated the in-efficiency of current machine implementations. The three Burroughs architectures represent solving this problem by building hardware aligned with high-level languages. The large systems were stack machines and very efficiently executed Algol. The medium systems (B2000,3000, and B4000) were aimed at the business world and executing Cobol (thus everything was done with BCD including addressing memory.) The B1000 series was perhaps the only "universal" solution from this perspective because it used idealized virtual machines for any language.
The actual hardware was built to enhance this capability. Perhaps the most obvious examples were the bit addressable memory, the variable size ALU, and the ability to OR in data from a register into the instruction register allowing very efficient instruction parsing. Another feature of the machine language was the appearance of having the output of the ALU appear as different addressable registers. X+Y, and X-Y are two read-only registers within the machine language.
One concession to the fact that Burroughs was primarily a supplier to business (and thus running Cobol) was the availability of BCD arithmetic in the ALU.
Internally the machines employed 16 bit instructions and a 24 bit data path. The bit addressable memory supported the mix quite efficiently. Internally, the later generation memories stored data on 32 bit boundaries, but were capable of reading across this boundary and supplying a merged result.
Notes
¹ ETM 313: Proper Language Processor for Small Systems (Bunker, et. al.), 1968. [link]
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