What Is Virtualization?
It’s important to start by defining the term virtualization. It means different things to different people when thinking about computing. For the purposes of this book, you can think of virtualization as breaking the bonds between different aspects of the computing environment, abstracting a certain feature or functionality from other parts. This abstraction and breaking of tight bonds provides great flexibility in system design and enables many of the current capabilities that are the focus of IT and this book.
Over time the “virtualization” tag was applied to many other technologies that had been around for some time, because they also broke those tight couplings and abstracted concepts. Over the next few pages I introduce the major types of virtualization, which are explored in detail throughout the book.
When the word virtualization is used without qualification, many people think of machine virtualization, which is the easiest to understand. With machine virtualization the abstraction occurs between the operating system and the hardware via a hypervisor. The hypervisor divides up the physical resources of the server, such as processor and memory, into virtual machines. These virtual (synthetic) machines have virtual hard disks, network adapters, and other system resources independent of the physical hardware. This means you can typically move a virtual machine fairly easily between different physical machines, as long as they use the same hypervisor. ...