Siemens SIMATIC S7-300 Manual page 58

Memory concept
6.2 Memory functions
Deleting blocks
When you delete a block, it is deleted from load memory. In
blocks with the user program (DBs also with SFC 23 "DEL_DB").
RAM used by this block is released.
Caution
If you delete a technology data block, the associated drive stops.
Remedy: Switch the CPU to STOP before you delete the technology data block.
Compression
When data are compressed, gaps which have developed between memory objects in load
memory/RAM as a result of load/delete operations will be eliminated. This releases free
memory in a continuous block.
Data compression is possible when the CPU is in RUN or in STOP.
Promming
When writing the RAM content to ROM, the actual values of the DBs are transferred from
RAM to load memory to form the start values for the DBs.
Note
This function is only permitted when the CPU is in STOP mode.
Load memory is cleared if the function could not be completed due to power loss.
6-12
STEP 7
, you can also delete
S7-300 CPU Data: CPU 315T-2 DP
Manual, 12/2005, A5E00427933-02