From SiriusIT.co.uk: 

1. Keeping pace with change

The Windows licence model assumes that the IT systems on which it runs is "fixed" in terms of its scale, and that the organisation using the software has relatively stable usage of the software. But virtualisation technologies used in networking and advances in the underlying hardware platforms have introduced a level of usage elasticity that make these licensing models redundant.

Only the Open Source software model - where licensing fees have given way to high-quality, commercial support - can keep pace with new advances in IT infrastructure and deliver tangible business benefits to the customer.

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