Virtualization as a concept

Virtualization is a computing approach that decouples hardware from software. It provides a better, more efficient, and programmatic approach to resource splitting and sharing between various workloads – virtual machines running OSes, and applications on top of them.

If we were to compare traditional, physical computing of the past with virtualization, we can say that by virtualizing, we get the possibility to run multiple guest OSes (multiple virtual servers) on the same piece of hardware (same physical server). If we're using a type 1 hypervisor (explained in Chapter 1, Understanding Linux Virtualization), this means that the hypervisor is going to be in charge of letting the virtual servers access physical hardware. This is because there is more than one virtual server using the same hardware as the other virtual servers on the same physical server. This is usually supported by some kind of scheduling algorithm that's implemented programmatically...