riporto la definizione di Cloud Computing secondo U.S. National Institute of Standards and Technology (NIST) :
• On-demand self-service: Individuals can obtain computing capabilities
such as server time or network storage on their own.
• Ubiquitous network access: Individuals can use standard network and
Internet devices, including mobile platforms, to access cloud resources.
• Location independent resource pooling: Computing resources are pooled
to serve multiple users, with different virtual resources dynamically assigned
according to user demand. The user generally does not know where the com-
puting resources are located.
• Rapid elasticity: Computing resources can be rapidly provisioned,
increased, or decreased to meet changing user demand.
• Measured service: Charges for cloud resources are based on amount of
resources actually used
Inoltre il Cloud computing consiste di tre differenti tipi di servizio :
• Cloud infrastructure as a service: Customers use processing, storage,
networking, and other computing resources from cloud service providers to
run their information systems. For example, Amazon uses the spare capacity
of its IT infrastructure to provide a broadly based cloud environment selling
IT infrastructure services. These include its Simple Storage Service (S3) for
storing customers’ data and its Elastic Compute Cloud (EC2) service for
running their applications. Users pay only for the amount of computing and
storage capacity they actually use.
• Cloud platform as a service: Customers use infrastructure and program-
ming tools hosted by the service provider to develop their own applications.
For example, IBM offers a Smart Business Application Development & Test
service for software development and testing on the IBM Cloud. Another
example is Salesforce.com’s Force.com, described in the chapter-ending case
study, which allows developers to build applications that are hosted on its
servers as a service.
• Cloud software as a service: Customers use software hosted by the vendor
on the vendor’s hardware and delivered over a network. Leading examples
are Google Apps, which provides common business applications online and
Salesforce.com, which also leases CRM and related software services over the
Internet. Both charge users an annual subscription fee, although Google
Apps also has a pared-down free version. Users access these applications
from a Web browser, and the data and software are maintained on the
providers’ remote servers
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