The Siemens 6ES7951-1AL00-0AA0 is a spare-part RAM Memory Card for the S7-300 programmable logic controller family. It provides 2 Mbyte of volatile RAM storage for user program blocks and data, in the short-design form factor that fits the standard S7-300 memory-card slot on the CPU or on the front-interface module.
The 2 Mbyte capacity determines how much user code and data the CPU can load. For an S7-300 CPU with a native memory limit below 2 MB, this card acts as a load memory extension; for a CPU that already has that capacity, it serves as a transport or backup medium. The RAM type means the card loses its contents when power is removed unless the CPU has a backup battery — so it is not a permanent program store like an FEPROM card.
This part carries a mature lifecycle status, meaning it is no longer in active new-production runs but remains available through the independent distribution channel.