Cloud computing has evolved through a number of phases which include grid and utility computing, application service provision (ASP), and Software as a Service (SaaS).
But the overarching concept of delivering computing resources through a global network is rooted in the sixties. The idea of an "intergalactic computer network" was introduced in the sixties by J.C.R. Licklider, who was responsible for enabling the development of ARPANET (Advanced Research Projects Agency Network) in 1969.
His vision was for everyone on the globe to be interconnected and accessing programs and data at any site, from anywhere, explained Margaret Lewis, product marketing director at AMD. "It is a vision that sounds a lot like what we are calling cloud computing."
Other experts attribute the cloud concept to computer scientist John McCarthy who proposed the idea of computation being delivered as a public utility, similar to the service bureaus which date back to the sixties.
Since the sixties, cloud computing has developed along a number of lines, with Web 2.0 being the most recent evolution. However, since the internet only started to offer significant bandwidth in the nineties, cloud computing for the masses has been something of a late developer.
One of the first milestones for cloud computing was the arrival of Salesforce.com in 1999, which pioneered the concept of delivering enterprise applications via a simple website. The services firm paved the way for both specialist and mainstream software firms to deliver applications over the internet.
The next development was Amazon Web Services in 2002, which provided a suite of cloud-based services including storage, computation and even human intelligence through the Amazon Mechanical Turk.
Then in 2006, Amazon launched its Elastic Compute cloud (EC2) as a commercial web service that allows small companies and individuals to rent computers on which to run their own computer applications.
"Amazon EC2/S3 was the first widely accessible cloud computing infrastructure service," said Jeremy Allaire, CEO of Brightcove, which provides its SaaS online video platform to UK TV stations and newspapers.
Another big milestone came in 2009, as Web 2.0 hit its stride, and Google and others started to offer browser-based enterprise applications, though services such as Google Apps.
"The most important contribution to cloud computing has been the emergence of "killer apps" from leading technology giants such as Microsoft and Google. When these companies deliver services in a way that is reliable and easy to consume, the knock-on effect to the industry as a whole is a wider general acceptance of online services," said Dan Germain, chief technology officer at IT service provider Cobweb Solutions.
Other key factors that have enabled cloud computing to evolve include the maturing of virtualisation technology, the development of universal high-speed bandwidth, and universal software interoperability standards, said UK cloud computing pioneer Jamie Turner.
Turner added, "As cloud computing extends its reach beyond a handful of early-adopter Google Docs users, we can only begin to imagine its scope and reach. Pretty much anything can be delivered from the cloud."
Following the cloud
"Many IT professionals recognise the benefits cloud computing offers in terms of increased storage, flexibility and cost reduction," said Songnian Zhou, chief executive officer of Platform Computing.
But he added that IT directors still have concerns about the security of their corporate data in the cloud. This means that it will be 2010 at the earliest before cloud adoption sees increased growth.
Julian Friedman, a specialist in emerging technologies, said that security and other concerns will soon be resolved.
"Considerations such as security, data privacy, network performance and economics are likely to lead to a mix of cloud computing centres both within the company firewall and outside of it."
He added that today's applications will naturally move towards a cloud model as they become more pervasively available through the web, require more data processing, and span the boundaries of multiple devices.
Experts seem to agree that cloud computing will ultimately transform today's computing landscape.
Andreas Asander, vice-principal of product management at virtualisation security specialist Clavister, said that once the security issues are resolved, cloud computing services "can enable an enterprise to expand its infrastructure, add capacity on demand, or outsource the whole infrastructure, resulting in greater flexibility, a wider choice of computing resources and significant cost savings." It is clear that cloud computing can bring enormous benefits for IT users.
However, the bottom line for IT directors is that they will need to continue to manage their internal computing environments, whilst learning how to secure, manage and monitor the growing range of external resources residing in the cloud.

1960-69:The  idea  of cloud  computing  started  to  emerge  before the  Internet  was invented.
1961: United States  computer  guru  John  McCarthy  ( inventor  of  the  term  artificial lintelligence, or AI ) first  suggested a vague model of a computer time sharing  system, which  was  the  early  stage  of  cloud computing.
1983: US  computer  company  Sun Microsystems  Inc  floated  the  idea  of  "the  network  isthe  computer".  However,  Sun  was  able  to  roll  out  only  one  product  based  on cloud computing  technology  in 2009,  before  Oracle Corp acquired it.
1997: IT  professor  Ramnath  Chellappa  was  the  first  to  use  " cloud  computing "  to describe  the  new  computing  system  that   relies on  cooperation  of  computers.  Hesuggested  that  the  cloud  would  be  a  new  " computing  paradigm  where  the  boundaries of  computing  will  be  determined  by  economic  rationale   rather than  technical  limitsalone."
2006: Web search company  Google  Inc ,  for  the  first  time,  shared  its  idea  of  cloud computing.  In  the  same  year,  Amazon. Com Inc  launched  one  of  the  world's  earliestonline  storage  services  named  Amazon  Simple  Storage  Service.  Amazon's  investmentin  the  area  has  paved  way  for the  company  to  become one of the biggest cloud-computing service providers globally.
2008: Chinese  companies  started  to  learn  how  the  new technology  could  benefit  their businesses.
2010: Cloud-computing  services  started  being  used  widely  in  the  consumer  market.
October 2011: Apple  Inc launched iCloud, a cloud-based  storage  service  for  Appleproduct  owners.  The  company  claimed  iCloud  has  more  than  150  million  users  as of July 2012.
In 2011: Chinese  e-commerce  giant  Alibaba  Group  Holding  Ltd  announced  plans  to develop  a  cloud-based  operating  system  for  smartphones.  The  move  was  seen  as Alibaba's  attempt to  tap  into  China's huge smartphone market.
Since 2011: The Chinese  government  has  reiterated  its  support  for  the  development of  the  cloud  computing  industry in China.