What this memory module does in an S7-200 rack
The Siemens 6ES7291-8GH23-0XA0 is the MC 291 memory module for the S7-200 family, specifically the S7-22X CPUs. It stores the project, handles data logging, and manages recipe data — all on a 256 kbyte Flash-EPROM that keeps the contents when the PLC loses power.
Why Flash-EPROM matters in a field-fix scenario
Flash-EPROM means the module retains the program and logged data without a battery backup — no ticking clock on the shelf, no worry about a dead lithium cell when you slot it into a replacement CPU on site. That 256 kbyte holds a fair-sized S7-200 project plus data logs; if you're swapping a failed CPU and the original memory card is gone, this spare part gets the line back up without a full download from a PC.
Marked as a spare part and carrying a current lifecycle stage, the 6ES7291-8GH23-0XA0 remains available through distribution.