Virtualization ≠ Cloud Computing
Let's get it right. Virtualization is about reducing the physical footprint of IT infrastructure and maximizing the utilization of the same. It helps to drastically reduce cumulative maintenance and onetime procurement costs of physical hardware. Since a virtualized environment (VE) is a logical representation of a physical environment hosted on real hardware and sandboxed, it makes practically possible to host multiple VEs on a single physical computer and an enterprise's business and IT applications can be consolidated on to fewer physical hardware:
Virtualization helps in reducing infrastructure complexity (less hardware), power (more green) and cuts overall operational overhead.
Cloud offers the same infrastructure & cost benefits of virtualization - reduced physical hardware and associated operational/maintenance overhead. Almost all the cloud service providers today have implemented their cloud platform using virtualization and that is what confuses people more about virtualization and cloud. Simply put, virtualization is one of the ways of implementing cloud. In other words, nothing stops one from implementing a cloud infrastructure with hundreds of blade servers instead of virtualization, for example. Not just that, cloud enables sharing compute power/resources - RAM, disk space, processors, network bandwidth from a central pool of those resources on-demand basis.
US Federal Government's National Institute of Standards and Technology (NIST) lists the following characteristics as essential for cloud model:
- On-demand self-service (cloud provisioning by consumers themselves)
- Broad network access (from a variety of/heterogeneous devices and software apps)
- Service usage to be measurable (monitoring & measuring resource usage - CPU, memory, disk space, network bandwidth, etc.)
- Elasticity (Cloud resources to be easily provisioned for increased & reduced load)
- Resource pooling (Computing resources pooled to be able to transparently share among multiple cloud consumers based on their demand)
As you can see, the above require capabilities much more than just virtualization part.
Think virtualization & cloud computing in parallel to classic ASP.NET web services & SOA. While ASP.NET web services are a means of realizing SOA, they are not SOA by themselves.