Fanuc A20B-2902-0371 ROM 4MB Memory board. Normally this memory pcb interfaces between Fanuc NC and MC.
Running the 18B control config in which it stores the system memory, ladder, and programs.
A20B-2902-0371 RAM memory pcb is available today, either as exchange or on an outright basis stock dependent with full testing and repair services are available also. Warranty is 180 days on repair or exchange!