Siemens SIMATIC PCS 7 CPU 410-5H System Manual page 58

I/O configuration variants
4.3 Fault-tolerant automation systems (redundancy operation)
Redundant I/O
Input/output modules are termed redundant when they exist twice and they are configured
and operated as redundant pairs. The use of redundant I/O provides the highest degree of
availability, because the system tolerates the failure of a CPU or of a signal module.
See also
Connecting redundant I/O to the PROFIBUS DP interface (Page 76)
58
CPU 410-5H Process Automation
System Manual, 09/2014, A5E31622160-AB