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Cloud Computing : Public or Private ?

Much of the debate about cloud computing has focused on two distinct types of operation: the public and private clouds. But although they are bundled under the convenient term of cloud computing, they are very different operational models.

Public started with Amazon

Public cloud, which is simply using the Internet to access computer services of one sort or another, has its roots in the decision by Amazon in 2002 to use its vast infrastructure to offer computer facilities to customers. The company launched a range of services to developers, including storage and a development platform.

Amazon's initiative, which preceded the phrase 'cloud computing' itself, has been followed by the likes of Google and a selection of hosting companies as they seek to capture the interest in this approach.

As if to demonstrate that there's nothing new under the sun, this is a throwback to the concept of the computer bureau, where companies paid a monthly fee to buy time on a mainframe. It's a business that had seemed to die a death when PCs and the client-server model came into play.

Like the computer bureaux, public cloud providers charge their customers on a monthly basis- generally according to gigabytes transmitted and bandwidth. The crucial aspect is that the cloud provider bears the entire cost of running the infrastructure, meaning that as a customer you do not have to worry about maintenance or staffing help desks. Nor do you have to worry about investing in storage hardware, a growing budgetary strain on organizations as data storage volumes move ever upwards.

Crucially, it also means that you do not have to worry about capacity planning. This can be a big headache for companies with seasonal fluctuations, where they might have over-provisioned for peak traffic. That's a headache that the new breed of cloud providers can deal with.

So, public cloud offers a number of advantages to organizations, particularly small businesses and start-ups, both of which may have no IT department and which may be reluctant to tie up capital on an IT infrastructure. There are, however, downsides too.

The main disadvantage with public cloud is that there are some security issues. Companies will have to hand over confidential data over to a third party and for many firms this is a move too far. There will be worries about customer data being released into the public domain, concerns about companies being held legally responsible for breaches of privacy legislation and worries about sensitive data being held on a server, particularly where two competitors might be hosted.

But if you're starting small, public cloud will almost certainly be the way to go as it will be able to handle something as small as say a basic client contact database for a couple of salespeople. And many providers offer simple storage services for single users.

In control with private cloud

The genesis of the private cloud was very different. There's no public operator and everything - hardware and software- is provided by you, the user. It sounds little different from a more conventional data center, where your servers and applications are hosted by a specialist provider. Indeed there are some commentators who claim that the idea of a private cloud is an oxymoron, and really we should be talking about data centers.

Proponents of private clouds maintain there is a difference: the main features of a private cloud are a 'virtualized' infrastructure coupled with software that allows IT users to treat that infrastructure as a centralized pool of computing resources.

Other features of the private cloud are automation, meaning that many of these tasks are handled without the intervention of an IT department, and the ability to measure and monitor what resources have been allocated to different departments, which could also means companies are able to introduce chargeback for resources that have been consumed.

In the private cloud set-up, you have responsibility for buying the hardware and software, maintaining it and managing storage. As such, private cloud doesn't offer so many advantages when it comes to managing cash flow.

But there are other advantages. You connect to public cloud providers by using Internet connections- these are, by their very nature, slow. This means that anyone trying to shift large files around would find the experience a lot of slower. On the other hand, private cloud infrastructures often use private connections, offering a much speedier experience, although there are issues for branch offices that may need to use a slower wide area network to get access to the main corporate link.

In addition, the private cloud doesn't have the security issues that could cause problems for public cloud users. All data is retained by your company and you control all access over a private 'firewall'.

What’s important here is that not only do you keep tabs on data - but you also know exactly where, geographically speaking, it's being held. This not an academic principle, as there are important legal restraints on where data can or cannot be held and companies have to be wary of their statutory duty for protecting customer information.

Why not go hybrid?

There's no need to choose between private and public, as organizations with more than basic needs for cloud IT can opt for both in a hybrid approach, with some services in a private cloud, others in a public one. This could still be managed by one provider and can address concerns such as holding sensitive data - such as customer credit card details- only on a private basis.

But you may be quite happy for staff to use say Twitter or Facebook- which are public cloud applications, after all - for customer communication, or any of the Google apps, such as Calendar and Docs, or say Salesforce.com, for communications among groups of staff, where ease of use is the foremost consideration.


  1. Less expensive than private clouds
  2. More accessible than private clouds
  3. Short-term or temporary commitments
  4. Faster to deploy a single user than private clouds
  1. Can be secured to meet compliance at almost every level
  2. Single tenant environments eliminate the possibility of other companies affecting performance
  3. Private data centres usually accessible to IT auditors
  4. Customisable to meet an individual organisation's needs, rather than the mass approach of public clouds
  1. Fewer user management controls
  2. One-size-fits all approach (not tailored to a single organization's or user's needs)
  3. Impersonal support, often via email, chat, or FAQs only
  4. Security and uptime might not meet enterprise compliance standards
  1. More expensive to deploy and maintain than public clouds
  2. May have longer-term commitments than public clouds
  3. May have less flexibility since hardware is dedicated to a single organisation