Virtio is a virtualization standard for network and disk device drivers where just the droplet's device driver "knows" it is running in a virtual environment, and cooperates with the hypervisor. This enables droplets to get high performance network and disk operations, and gives most of the performance benefits of paravirtualization.
TL;DR: VirtIO is a better virtualization driver that enables better network/disk performance.
I think VirtIO is interfering with my php uploads. I find it impossible to upload larger files. I have made all of the required changes to php.ini but still not luck. I have tried using nginx and apache. VirtIO seems to be the last variable to eliminate.