Single Root I/O Virtualization is a PCIe specification that lets one physical device expose a Physical Function (PF) plus many lightweight Virtual Functions (VFs). A hypervisor can assign VFs directly to virtual machines or containers, which then perform I/O without the hypervisor on the data path. For NICs this yields near-bare-metal network performance with low CPU overhead, at the cost of less flexibility than fully software-virtualized I/O.