The Siemens 6ES7954-8LF00-0AA0 is a SIMATIC S7 memory card for the S7-1200 CPU, storing the user program and data on 24 Mbyte of Flash-EPROM at 3.3 V NFLASH. That 24 Mbyte capacity determines how large a project — including code, tags, and configuration data — the CPU can hold; for a mid-size line with a few hundred I/O points and basic recipe management, this is the typical headroom. The Flash-EPROM type means the program is retained without battery backup across power cycles, so no reload after a power loss.
This part carries a mature lifecycle stage, meaning it's a stable, long-available product — not newly introduced, not on phase-out notice.