Private vs. Public Cloud

So, the other day my boss and peers were kicking the tires around cloud computing during a staff meeting.  

The questions came up "Are we cloud computing simply because we've built a web application and hosted it on an internal IIS server?" and "Does that make it a private cloud?" and "If not, then what constitutes a private cloud?"  Unfortunately, none of us knew the answer.

So can anyone best explain the difference between a private and public cloud?  
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Paul MacDonaldDirector, Information SystemsCommented:
If you have a web farm (and maybe a database cluster) you could say you have a private cloud.  I think most people would equate a cloud with virtualized machines and services moreso than physical ones, but there's no real differentiation.
the line between internal application hosting and "private cloud" is a fine line and everybody will have their own opinion.

public cloud is easy. public cloud are services like gmail, or microsoft office 365, or amazon's virtual server hosting. they are applications, frameworks, infrastructure, or services hosted in the public realm by a company that is not the targeted client in a web-application format.

a private cloud is essentially the same thing, but it is hosted by the intended client. such as if you had a group of companies that are all managed by a parent company, and all of the smaller companies use the same parent company's web mail server, with their own domain. a private datacenter which is entirely run on a virtualization platform such as vmware, citrix, or hyperV would largely fit in this category. larger companies and SMB on the leading/bleeding edge would be under this group

private application hosting would be if the smaller companies host their own application, eg is hosted on a different server from

in reality the word "cloud" has become a buzzword in the industry, among the more business oriented folks in the IT world, and has largely lost its meaning. Stick with phrases like "custom application which is tailor made to suit our business needs" and you cannot go wrong.

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Private Cloud - Running VDI or Hypervisors internally

Public Cloud - Using hosting companies to host your email, storage, web services, possibly even an entire datacenter.
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sk1922Author Commented:
>>private application hosting would be if the smaller companies host their own application, eg is hosted on a different server from


Thank you for the explanation.  Can you elaborate a bit on this; I am assuming that the "smaller companies" are virtualized and under the context of their "own" application domain?
Just trying to gain further clarity on the point.  

Cloud is just an Architecture. Hence no exact definition exists
At high level we can say when infrastructure is privately maintained like datacenter or cluster (mainly due to security, privacy ,confidentiality ) and access is only available internal members then we call it as a private cloud.
Taking one example to show why private cloud is required
As in Banking domain, every transaction and data is very critical so no would like to store it an unknown place which cannot be tracked that where exactly it is stored. So to gain better data management & services virtual cloud architecture is used

Daniel WilsonCommented:
"Cloud" involves virtualization, AFAIK.  The "elastic" ability to provision more resources on demand is, I believe, the exclusive domain of virtual machines running under hypervisers that support it.
sk1922Author Commented:
both very concise answers
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