Fanuc A20B-1006-0260 is 2-slot backplane PCB for large CNC’s. Belonging to the Fanuc series 21-TB control systems. This board is inserted into the yellow plastic frame which holds each board in place to connect the control system together. The MAIN is normally in the left slot and the I/O PSU which is the I-O for the system with a bolt on PSU in the right. Then its a mixture of boards dependent on what type of CNC machine tool.