The document outlines differences between various Cisco operating systems: IOS, IOS-XE, IOS-XR, NX-OS, and CATOS. Each operating system has distinct features and architectural designs, such as IOS being monolithic, IOS-XE using a Linux kernel, and IOS-XR emphasizing high availability and scalability. CATOS is a legacy system no longer in widespread use, while NX-OS is tailored for Nexus-series switches with a similar CLI to IOS.