Siemens SIMATIC PCS 7 Function Manual page 14

Basics of Fault Tolerance
2.1 Rationale for using fault-tolerant process control systems
Legend for the above illustration:
Note
The following short designations are commonly used in this documentation.
Short designation
Engineering Sta‐
tion
OS server
14
PS CPU
CPCPCPCPCP
PS PS IM
PS PS IM
Meaning
Engineering station, PC
Operator station, PC project data station in the project form "WinCC Server"
PS CPU
CPCPCPCPCP
IM SM SM SM
IM SM SM SM
Fault-tolerant Process Control Systems (V8.1)
Function Manual, 11/2014, A5E34878832-AA
SM SM SM
SM SM SM