Memory concept   
4.1 Memory areas and retentivity 
  CPU 31xC and CPU 31x, Technical Data 
4-8  Manual, 01/2006 Edition, A5E00105475-06 
4.1.5  Properties of the SIMATIC Micro Memory Card (MMC) 
The SIMATIC Micro Memory Card (MMC) as memory module for the CPU 
The memory module used on your CPU is a SIMATIC Micro Memory Card. You can use 
MMCs as load memory or as a portable storage medium. 
 
 
Note 
The CPU requires the SIMATIC Micro Memory Card for operation. 
 
The following data are stored on the SIMATIC Micro Memory Card. 
•  User programs (all blocks) 
•  Archives and recipes 
•  Configuration data (STEP 7 projects) 
•  Data for operating system update and backup 
 
 
 
Note 
You can either store user and configuration data or the operating system on the SIMATIC 
Micro Memory Card. 
 
Properties of the SIMATIC Micro Memory Card (MMC)  
The SIMATIC Micro Memory Card ensures maintenance-free and retentive operation of 
these CPUs. 
 
 
Caution 
Data on a SIMATIC Micro Memory Card can be corrupted if you remove the card while it is 
being accessed by a write operation. In this case, you may have to delete the SIMATIC 
Micro Memory Card on your PG, or format the card in the CPU. Never remove a SIMATIC 
Micro Memory Card in RUN mode. Always remove it when power is off, or when the CPU is 
in STOP state, and when the PG is not writing to the card. When the CPU is in STOP mode 
and you cannot not determine whether or not a PG is writing to the card (e.g. load/delete 
block), disconnect the communication lines.