Virtio

Virtio is a standardized paravirtualized I/O framework that defines a common interface between virtual machines and hypervisors for network, disk, and other device access. Originally developed for the KVM ecosystem but now adopted by Xen, VMware, and major cloud providers, virtio replaces slow hardware emulation with cooperative guest-hypervisor communication through shared-memory ring buffers. The framework's standardization breaks the vendor lock-in that plagued earlier virtualization: a single virtio driver in the guest OS can work with any hypervisor that implements the virtio backend. Yet virtio also exposes an irreducible tension in systems design: the guest must know it is virtualized, sacrificing the transparency that full emulation promised in exchange for performance that emulation cannot deliver.

— Virtio is the systems community's admission that honesty outperforms illusion. The paravirtualized guest knows it is not on real hardware, and that knowledge is precisely what makes it fast.