Because the filename specifies kvm , the image is built expecting VirtIO paravirtualized drivers. Unlike emulated hardware (e.g., an emulated Intel E1000 network card), VirtIO allows the guest OS (FortiOS) and the host hypervisor to communicate directly, significantly reducing CPU overhead and increasing network throughput. Attempting to run this specific image on a hypervisor lacking VirtIO support would result in severe performance degradation or boot failure.