What it is and what it does
The Siemens 6ES7953-8LF10-0AA0 is a Micro Memory Card for the SIMATIC S7 family, specifically the S7-300, C7, and ET 200S IM151 CPU. It provides 64 KB of NFLASH storage, operating at 3.3 V, for loading and storing the user program, configuration data, and firmware updates. The card plugs directly into the CPU's memory-card slot and is recognized at power-up.
Integration note
The card is keyed for the S7-300 CPU slot — it will not physically fit S7-1200 or S7-1500 CPUs. Insertion direction is marked on the card; the CPU's access cover must be open. The 3.3 V NFLASH technology means the card is not hot-swappable — power down the CPU before inserting or removing. After insertion, the CPU reads the card at boot and copies the program into its internal RAM; the card remains as a backup store.