| Memory Area | Purpose | S7-DOS Mechanism | |-------------|---------|------------------| | Load memory (RAM/Flash) | User program code, blocks | File‑like block storage | | Work memory (RAM) | Runtime copies of code+data | iRMX segments | | System memory | OBs, SDBs, link data | Kernel dynamic allocation | | Retentive memory | Remanent data markers, counters | Battery‑backed, checksummed |
| Protocol | Task | Priority | |----------|------|----------| | MPI | S7‑DOS task (low) | Cyclic | | PROFIBUS DP master | Background interrupt | High | | PROFINET (later) | Ethernet task | Mixed | simatic s7dos
S7-DOS guarantees that a higher priority OB preempts a lower one – true preemptive RTOS, not a cooperative loop. S7-DOS implements a segmented memory model with hardware protection (using MC683xx/Intel 80186 memory management units). | Memory Area | Purpose | S7-DOS Mechanism