The 1784-CF128 a ControlNet Fiber Media Module with 128K Words of Memory.
The memory card 1784-CF128 is a specific type of memory card commonly used in Rockwell Automation's Allen-Bradley ControlLogix programmable logic controllers (PLCs). This CompactFlash (CF) memory card has a capacity of 128 megabytes (MB).
CF memory cards are used to store program files, configuration data, and other information required by the PLC for operation. The 1784-CF128 card can be inserted into the designated slot on the ControlLogix PLC, allowing the PLC to access the stored data.