Short answers, pulled from the story.
COMPASS stands for COMPrehensive ASSembler. It is a family of macro assembly languages used on Control Data Corporation's 3000 series and on the 60-bit CDC 6000 series, 7600, and Cyber 70 and 170 series mainframes.
COMPASS is a classical two-pass assembler with macro and conditional assembly features. It generates a full listing that shows both the source assembly code and the generated machine code in octal.
COMPASS CP is the assembly language for the Central Processor, which runs user programs, while COMPASS PP is the assembly language for the Peripheral Processor, which runs only operating system code. Peripheral processor instructions are completely different from central processor instructions.
The central processor maintains 24 operational registers named A0 to A7, X0 to X7, and B0 to B7. The X registers are 60 bits long and hold data, while the A and B registers are 18 bits long.
Setting an address into any of A1 through A5 loads the data at that memory location into the corresponding X register, while setting an address into A6 or A7 stores the contents of X6 or X7 to that location. A0 can hold any address without affecting the contents of X0.
CDC's operating systems were written almost entirely in COMPASS assembly language. Peripheral processor programs could be assembled without special job validation but had to be installed into the operating system through special system editing commands before they could execute.