All in Operations & Infrastructure
An Introduction to Virtualization
The IT industry makes heavy use of buzzwords and ever changing terms to define itself. Sometimes the latest nomenclature the industry uses is a particular technology such as x86 or a concept such as green computing. Terms rise and fall out of favor as the industry evolves. In recent years the term virtualization has become the industry’s newest buzzword. This raises the question … just what is virtualization? The first concept that comes to the mind of the average industry professional is running one or more guest operating systems on a host. However, digging a little deeper reveals this definition is too narrow. There are a large number of services, hardware, and software that can be “virtualized”. This article will take a look at these different types of virtualization along with the pros and cons of each. What is virtualization?
Before discussing the different categories of virtualization in detail, it is useful to define the term in the abstract sense. Wikipedia uses the following definition: “In computing, virtualization is a broad term that refers to the abstraction of computer resources. Virtualization hides the physical characteristics of computing resources from their users, be they applications, or end users. This includes making a single physical resource (such as a server, an operating system, an application, or storage device) appear to function as multiple virtual resources; it can also include making multiple physical resources (such as storage devices or servers) appear as a single virtual resource...” In layman’s terms virtualization is often:
1. The creation of many virtual resources from one physical resource. 2. The creation of one virtual resource from one or more physical resource. The term is frequently used to convey one of these concepts in a variety of areas such as networking, storage, and hardware. History
Virtualization is not a new concept. One of the early works in the field was a paper by Christopher Strachey entitled "Time Sharing in Large Fast Computers". IBM began exploring virtualization with its CP-40 and M44/44X research systems. These in turn lead to the commercial CP-67/CMS. The virtual machine concept kept users separated while simulating a full stand-alone computer for each. In the 80’s and early 90’s the industry moved from leveraging singular mainframes to running collections of smaller and cheaper x86 servers. As a result the concept of virtualization become less prominent. That changed in 1999 with VMware’s introduction of VMware workstation. This was followed by VMware’s ESX Server, which runs on bare metal and does not require a host operating system. Types of Virtualization
Today the term virtualization is widely applied to a number of concepts including:
Client / Desktop / Application Virtualization
Service / Application Infrastructure Virtualization
In most of these cases, either virtualizing one physical resource into many virtual resources or turning many physical resources into one virtual resource is occurring. Server Virtualization
Server virtualization is the most active segment of the virtualization industry featuring established companies such as VMware, Microsoft, and Citrix. With server virtualization one physical machine is divided many virtual servers. At the core of such virtualization is the concept of a hypervisor (virtual machine monitor). A hypervisor is a thin software layer that intercepts operating system calls to hardware. Hypervisors typically provide a virtualized CPU and memory for the guests running on top of them. The term was first used in conjunction with the IBM CP-370. Hypervisors are classified as one of two types:
Type 1 – This type of hypervisor is also known as native or bare-metal. They run directly on the hardware with guest operating systems running on top of them. Examples...
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