Fork is not a language feature though, it's an operating system feature. It just so happens that it feels that way because it's so universal in multi-process s

Fork is not a language feature though, it's an operating system feature. It just so happens that it feels that way because it's so universal in multi-process systems. The reality is that there are many uni-process systems, like embedded microcontrollers etc. Unikernels actually have a lot in common with these sorts of environments. For instance if you are running a unikernel on PV Xen or KVM you have direct access to the paravirtualized network and block device buffers, avoiding additional context switches when doing IO (this is where those 10x speedups from from). Thing is though you can achieve the same performance on more traditional OS + multi-process setups too but it does require some level of device level virtualisation + isolation and kernel bypass. For instance combining PCI SRIOV with say PF_RING would give you effectively the same performance profile without sacrificing OS level features.