COMPASS

COMPASS, COMPrehensive ASSembler, is any of a family of macro assembly languages for Control Data Corporation's 3000 series, and for the 60-bit CDC 6000 series, 7600 and Cyber 70 and 170 series mainframe computers. While the architectures are very different, the macro and conditional assembly facilities are similar. COMPASS for 60-bit machines There are two flavors of COMPASS on the 60-bit machines: COMPASS CP is the assembly language for the CP (Central Processor), the processor running user programs. See CDC 6600 CP architecture. COMPASS PP is the assembly language for the PP (Peripheral Processor), only running operating system code. See CDC 6600 PP architecture. COMPASS is a classical two-pass assembler with macro and conditional assembly features, and generates a full listing showing both the source assembly code and the generated machine code (in octal). CDC's operating systems were written almost entirely in COMPASS assembly language. Central processor (CP or CPU) hardware maintains 24 operational registers, named A0 to A7, X0 to X7 and B0 to B7. Registers X0 to X7 are 60 bits long and are used to hold data, while registers B0 to B7 are 18 bits long and their major purpose is to hold either addresses or be used as indexing registers, except that B0 is always zero. As a programming convention, B1 (or B7) often contains positive 1.