The Burroughs B1000 Series was a series of mainframe computers, built by the Burroughs Corporation, and originally introduced in the 1970s with continued software development until 1987. The series consisted of three major generations which were the B1700, B1800, and B1900 series machines. They were also known as the Burroughs Small Systems, by contrast with the Burroughs Large Systems (B5000, B6000, B7000, B8000) and the Burroughs Medium Systems (B2000, B3000, B4000). Much of the original research for the B1700, initially codenamed the PLP ("Proper Language Processor" or "Program Language Processor"), was done at the Burroughs Pasadena plant. 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. Features Writeable control store The B1000 is distinguished from other machines in that it had a writeable control store allowing the machine to emulate any other machine. The Burroughs MCP (Master Control Program) would schedule a particular job to run. The MCP would preload the interpreter for whatever 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 inefficiency of current machine implementations. The three Burroughs architectures represent solving this problem by building hardware aligned with high-level languages, so-called language-directed design (contemporary term; today more often called a "high-level language computer architecture"). 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 arithmetic logic unit (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. Internals One concession to the fact that Burroughs was primarily