Solution

Para virtualization is preferred when performance optimization is crucial, as it minimizes overhead by allowing guest operating systems to interact directly with the hypervisor. In para virtualization, guest OSes are aware of the virtualization and can make calls to the hypervisor for specific operations, reducing the emulation overhead present in full virtualization. This direct interaction leads to improved performance for I/O operations and system calls, making it particularly useful in data centers and environments where resource efficiency is vital. However, the requirement for modifying the guest OS can limit its applicability to certain workloads. Why Other Options are Incorrect: A) When complete isolation between guest operating systems is required: Full virtualization provides better isolation as it fully emulates the hardware for each guest OS. B) When running legacy applications unmodified: Full virtualization allows unmodified legacy applications to run without any changes, which is not possible with para virtualization. D) When hardware emulation is necessary: Full virtualization emulates all hardware components, making it suitable for scenarios that require comprehensive hardware simulation. E) When a single operating system is sufficient: This scenario does not warrant virtualization in any form, as it can run directly on physical hardware without the need for any virtualization techniques.