What is virtual machine (VM)?

A virtual machine (VM) is an environment, usually a program or operating system, which does not physically exist but is created within another environment. In this context, a VM is called a "guest" while the environment it runs within is called a "host." Virtual machines are often created to execute an instruction set different than that of the host environment. One host environment can often run multiple VMs at once. Because VMs are separated from the physical resources they use, the host environment is often able to dynamically assign those resources among them.

The phrase "virtual machine" is commonly used to describe Java runtime environment, the Java Virtual Machine (JVM), in which Java-specific commands are interpreted. The JVM is a virtual machine in that it executes code compiled specifically for it – known as bytecode – and abstracts use of resources for this bytecode. The Java programming language does not rely on platform-specific instruction sets, such as APIs specific to any one operating system, to display output or access resources such as files. Instead, the JVM creates virtualized resources which the bytecode accesses. These actions are then passed on to the machine's actual resources.

A user interacting with a virtualized server can view the server as a physical machine, in the sense that the user would see access to machines resources like hard disks, RAM, processors and Ethernet connections. In fact, all of these machine resources are virtual. For instance, instead of accessing a real hard disk, the user is accessing a construct of the host environment. This construct then accesses the real disk to record the data.

"A running program is often referred to as a virtual machine - a machine that doesn't exist as a matter of actual physical reality. The virtual machine idea is itself one of the most elegant in the history of technology and is a crucial step in the evolution of ideas about software. To come up with it, scientists and technologists had to recognize that a computer running a program isn't merely a washer doing laundry. A washer is a washer whatever clothes you put inside, but when you put a new program in a computer, it becomes a new machine. . . The virtual machine: A way of understanding software that frees us to think of software design as machine design." -From David Gelernter's "Truth, Beauty, and the Virtual Machine," Discover Magazine, September 1997, p. 72.

What is private cloud (internal cloud or corporate cloud)?

What is a private cloud?

Private cloud (also called internal cloud or corporate cloud) is a marketing term for a proprietary computing architecture that provides hosted services to a limited number of people behind a firewall.

Advances in virtualization and distributed computing have allowed corporate network and datacenter administrators to effectively become service providers that meet the needs of their "customers" within the corporation.

Marketing media that uses the words "private cloud" is designed to appeal to an organization that needs or wants more control over their data than they can get by using a third-party hosted service such as Amazon's Elastic Compute Cloud (EC2) or Simple Storage Service (S3). 

What is service-oriented architecture (SOA)?

A service-oriented architecture (SOA) is the underlying structure supporting communications between services. SOA defines how two computing entities, such as programs, interact in such a way as to enable one entity to perform a unit of work on behalf of another entity. Service interactions are defined using a description language. Each interaction is self-contained and loosely coupled, so that each interaction is independent of any other interaction.

Simple Object Access Protocol (SOAP)-based Web services are becoming the most common implementation of SOA. However, there are non-Web services implementations of SOA that provide similar benefits. The protocol independence of SOA means that different consumers can communicate with the service in different ways. Ideally, there should be a management layer between the providers and consumers to ensure complete flexibility regarding implementation protocols.

Whether you realize it or not, you've probably relied upon SOA, perhaps when you made a purchase online. Let's use Land's End as an example. You look at their catalog and choose a number of items. You specify your order through one service, which communicates with an inventory service to find out if the items you've requested are available in the sizes and colors that you want. Your order and shipping details are submitted to another service which calculates your total, tells you when your order should arrive and furnishes a tracking number that, through another service, will allow you to keep track of your order's status and location en route to your door. The entire process, from the initial order to its delivery, is managed by communications between the Web services -- programs talking to other programs, all made possible by the underlying framework that SOA provides.