a merger in which Burroughs acquired Sperry Corporation and changed its name to Unisys, the company continued to develop new machines based on the MCP CMOS ASIC. These machines were the Libra 100 through the Libra 500, With the Libra 590 being announced in 2005. Later Libras, including the 590, also incorporate Intel Xeon processors and can run the Burroughs large systems architecture in emulation as well as on the MCP CMOS processors. It is unclear if Unisys will continue development of new MCP CMOS ASICs. Primary lines of hardware Hardware and software design, development, and manufacturing were split between two primary locations, in Orange County, California, and the outskirts of Philadelphia. The initial Large Systems Plant, which developed the B5000 and B5500, was located in Pasadena, California but moved to City of Industry, California, where it developed the B6500. The Orange County location, which was based in a plant in Mission Viejo, California but at times included facilities in nearby Irvine and Lake Forest, was responsible for the smaller B6x00 line, while the East Coast operations, based in Tredyffrin, Pennsylvania, handled the larger B7x00 line. All machines from both lines were fully object-compatible, meaning a program compiled on one could be executed on another. Newer and larger models had instructions which were not supported on older and slower models, but the hardware, when encountering an unrecognized instruction, invoked an operating system function which interpreted it. Other differences include how process switching and I/O were handled, and maintenance and cold-starting functionality. Larger systems included hardware process scheduling and more capable input/output modules, and more highly functional maintenance processors. When the Bxx00 models were replaced by the A Series models, the differences were retained but no longer readily identifiable by model number. ALGOL The Burroughs large systems implement an ALGOL-derived stack architecture. The B5000 was the first stack-based system. While B5000 was specifically designed to support ALGOL, this was only a starting point. Other business-oriented languages such as COBOL were also well supported, most notably by the powerful string operators which were included for the development of fast compilers. The ALGOL used on the B5000 is an extended ALGOL subset. It includes powerful string manipulation instructions but excludes certain ALGOL constructs, notably unspecified formal parameters. A DEFINE mechanism serves a similar purpose to the #defines found in C, but is fully integrated into the language rather than being a preprocessor. The