The Siemens 6ES7951-0KE00-0AA0 is a 32 kbyte Flash-EPROM memory card for the S7-300 family. It's a 5V short-design spare part that stores and transfers the PLC program and data blocks. This card plugs directly into the memory-card slot on S7-300 CPUs. It's the part you reach for when the original card fails or you need to load a program revision on a spare CPU without a PG connection.
Memory type and capacity
32 kbyte of Flash-EPROM means the program survives a power cycle without a battery backup. That's enough for a compact machine sequence or a small process cell — think a single conveyor zone or a packaging station with a few dozen rungs.