Technical data

Appendix
27.2 Memory Areas of S7 CPUs
Programming with STEP 7
Manual, 05/2010, A5E02789666-01 571
27.2 Memory Areas of S7 CPUs
27.2.1 Distribution of the Memory Areas
The memory of an S7 CPU can be divided into three areas (see figure below):
• The load memory is used for user programs without symbolic address assignments or
comments (these remain in the memory of the programming device). The load memory can be
either RAM or EPROM.
• Blocks that are not marked as required for startup will be stored only in the load memory.
• The work memory (integrated RAM) contains the parts of the S7 program relevant for running
your program. The program is executed only in the work memory and system memory areas.
• The system memory (RAM) contains the memory elements provided by every CPU for the user
program, such as the process-image input and output tables, bit memory, timers, and counters.
The system memory also contains the block stack and interrupt stack.
• In addition to the areas above, the system memory of the CPU also provides temporary
memory (local data stack) that contains temporary data for a block when it is called. This data
only remains valid as long as the block is active.