Hyperkit is a hypervisor. Virtualbox is a hypervisor. Hyper-V is a hypervisor. VMWare products are hypervisors. They are all hypervisors, a hypervisor is just t

Hyperkit is a hypervisor. Virtualbox is a hypervisor. Hyper-V is a hypervisor. VMWare products are hypervisors. They are all hypervisors, a hypervisor is just the platform that manages the virtualisation (which is a CPU feature). What changes is what parts of the host system are emulated and the manner in which system peripherals are passed through. The only alternative to a hypervisor that you could mean is full-system emulation, e.g. some modes of QEMU where the CPU itself is emulated on top of another system. This is obviously slow. Virtualised OS are obviously "slightly" slower because they now don't have 100% of a system to use, and usually require a dedicated chunk of the system RAM, but usually what people actually mean by saying they are slower is because often they don't have direct hardware peripheral access (e.g. their own dedicated network card and disk drives) and the hypervisor emulates some amount of the system. This is the case with the most accessible linux VMs that run docker, because simulating the block devices on top of the MacOS filesystem is slow. Docker itself is none of these, it's a fancy chroot enabled by linux kernel features, so _requires_ running on top of linux or a sufficiently linux-like compatibility layer. So you see why it's somewhat incoherent and makes it sound like you are talking out of your ass when you complain that Hyperkit is a hypervisor but "Virtual machines aren't", but all these horrible people keep disagreeing with you.