The FANUC A20B-3900-0074 is a 4M FROM system memory module for compatible FANUC i-Series CNC controls. Installed in a dedicated DIMM socket on the CNC motherboard, it provides non-volatile storage for CNC and servo system software.

Some parts listings describe it as a 4MB program memory card or Program Memory C. FANUC maintenance documentation identifies its formal hardware type as a FROM module, which is different from the adjacent SRAM module used for system data.

A20B-3900-0074 Product Information

FROM Module Function

A20B-3900-0074 stores the installed CNC and servo system files required by the matching control configuration. It should not be confused with an SRAM module, DRAM module or removable operator program card. A correctly sized module without the correct system software may not start or operate the machine correctly.

Compatibility and Software Checks

Confirm the complete A20B-3900-0074 number, module revision, motherboard, CNC series and installed software version. FANUC also documents A20B-3900-0014 in the 4M FROM category, but matching capacity alone does not prove direct interchangeability. Confirm the machine builder's software package and option configuration before replacement.

Testing and Installation Notes

REACO CNC checks the label, contacts, PCB condition, module recognition and system startup under an applicable test setup. Back up all accessible CNC parameters, programs, offsets, PMC data and machine-builder files before replacement. Installation should be performed with CNC power isolated and proper ESD protection.

Related resources: FANUC PCB boards, FANUC CNC controls and FANUC CNC repair services.