There are already built-in 1700 words of EEPROM memory in the M-series PLC which can be used to store the user's data using the SAVE_EEP or SAVE_EEP$ command. Upon power on you can use the LOAD_EEP command to load the data back into the PLC.
If you purchase the optional M2018P module, you can have access to 7700 words of EEPROM data memory and 8190 words of program memory.
One other way is to connect the PLC to the PC using RS232 port and run the TLServer. You can then use the PRINT #1 <WRITE filename> to open a file on the PC and save the data to the PC. The data can be read back into the PLC using the <READ filename> command.