Virtio is the framework which improves VPS disk I/O and network performance much better compared to full virtualization.
KVM, the virtualization type used by Z.com VPS, support both full virtualization and half virtualization.
After you add an VPS, you will be able to turn ON/Off the function on the [Network Virtio] and the [Storage Virtio].
ON will run full virtualization, and off to run half virtualization.