Siemens SIMATIC ET 200S Manual page 129

Compression
Compression fills any gaps between memory objects which are formed by loading
and erasing operations in the load and working memory. Contiguous areas of free
memory are then available.
Compression is possible when the CPU is in both the STOP and RUN mode.
Promming (RAM to ROM)
With promming, the current values of the data blocks are transferred from the
working memory to the load memory where they serve as new initial values for the
DB.
Note
The function is only permitted when the CPU is in STOP mode.
The load memory remains empty if the function could not be completed owing to a
power failure.
ET 200S IM 151-7 CPU Interface Module
A5E00058783-04
Functions of the IM 151-7 CPU
8-17