Cloud platforms where you can rent a bare Windows / Linux server with scalable power. Examples: Amazon Web Services, Rackspace Cloud.
Cloud platforms with all the necessary middleware and auxiliary software (DBMS, framework, services). Examples: Windows Azure, Force.com.
Business applications delivered as Internet services. Examples: Google Apps, Salesforce CRM.
Some companies want to take advantage of Cloud Computing, but are afraid to host their IT infrastructure on other people’s servers. Resourceful IT vendors came up with “Private clouds” for such companies.
At the same time, company buys computer resources (servers) and, using virtualization technologies, combines them into “clouds”. At the same time, an economic effect is achieved by optimizing the load on each server. However, this effect is not comparable with option of renting computer resources from a third-party provider.
But, having built its own private cloud, a company can easily transfer its IT infrastructure to a third-party cloud platform.