The 6ES7951-1AH00-0AA0 is a spare-part RAM Memory Card for the Siemens S7-300 PLC family, carrying 256 kbyte of volatile memory in a short-design form factor.
The memory type is RAM, which means it holds the program and data only while the S7-300 CPU is powered and the backup battery is good. Unlike an FEPROM card, the RAM card does not retain contents after a power loss without a battery-backed CPU slot. This is the card you load a working program into for commissioning or for a hot spare swap — not the one you store the master copy on.
This part is classified at a mature lifecycle stage. That means it is not in active new-production runs from Siemens, but it remains available through the independent channel for as long as the S7-300 installed base needs it. If you are holding a spare for a critical S7-300 line, this is exactly the card to keep in the cabinet — before it fails.
Physical fit and handling
At 38 g and a short-design profile, this card fits the standard S7-300 memory card slot on any CPU that accepts the short format. No special tools or adapters needed — it slides into the front-panel slot and locks. The RAM type means you will need to reload the program after any extended power-down unless the CPU battery holds.