hypervisor
termcloud
The layer that presents virtual hardware to several operating systems and keeps them apart.
It is the strongest common isolation boundary in ordinary infrastructure, because each guest has its own kernel and the hypervisor mediates the hardware - which is why multi-tenant cloud is built on it rather than on containers alone. The cost is that it is also the most privileged software present: whatever compromises it owns every guest at once, and the guests cannot detect that. Side channels through shared processor resources are the awkward part, because they cross a boundary the design assumed was solid.
Also known as: vmm, type 1, type 2