Question: what is the difference between cisco ios and ios xr?
Answer: IOS vs. IOS XR is based on QNX (since version 5.0 it's also based on linux) where the IOSd application has been separated into many different applications. While IOS XE (IOSd) and IOS share a lot of the same code, IOS XR is a completely different code base. ... Another example is the Cisco IOS XE Open Service Containers.