The excerpts below  are from Wikipedia and substantiate a position I have held for many years regarding both the TCO of Linux vs. Windows Server and the depths to which Microsoft will sink in its pursuit of market dominance.

Cybersource TCO study: Linux versus Windows

Melbourne-based Cybersource compared in 2004 the Total Cost of Ownership (TCO) of running Linux versus Windows in the enterprise. Its studies found that Linux was 36% cheaper than Windows, when taking into account the software cost as well as service, support and upgrades. The study done in 2004 was an update on their previous studies in 2002, and found the same results.

I believe that in small deployments, Linux may be as much as 65-75% cheaper in three-year TCO than Windows Server, when you factor in the cost per user--consider the following:

For any number of users up to hardware performance limitations (let's just use 150), a Dell PowerEdge 1850 costs about $2,500 and RHEL costs ~$900/yr (for updates and support)--thus the HW and SW over three years is ~$5,500.

For 15 users, a Dell PowerEdge 1850 costs about $2,500 and Windows Server 2008 costs ~$1,400, MS SQL ~$3,000, & Terminal Services Licensing ~$1,400. The added MS software as you can see, costs ~$6,000 for a base deployment of only 15 seats--thus the HW and SW over three years with The Evil Emipre is ~$8,500 or $3,000 more than RHEL for 1/10 as many users.

Thusfar we have examined only the HW and SW components of three-year TCO--here's where the rubber meets the road--the total number of service hours spent on a RHEL box over a 3-year period is less than 30. For a Windows deployment the number is easily two to three times higher, but most importantly, we must remember that in the case of the Windows deployment we are only serving 15 users making our cost per user of the Windows platform increase over RHEL by at least a factor of ten.

"Get the Facts"

Get the Facts was an ongoing advertising campaign launched by Microsoft in 2004 to convince users to switch from Linux to Windows servers. It was originally focused on comparing the total cost of ownership (TCO) of Linux to Windows, but later compared reliability, security and interoperability. Microsoft claims that its products have a lower overall TCO than open source programs, proposing that the Windows server platforms offered improved ease of use leading to these savings.

As part of the "Get the Facts" campaign Microsoft highlighted the .NET trading platform that it had developed in partnership with Accenture for the London Stock Exchange, claiming that it provided "five nines" reliability. After suffering extended downtime and unreliability the LSE announced in 2009 that it was planning to dump Microsoft and switch to Linux in 2010.

Response

Microsoft's figures are disputed by a variety of organisations, notably Novell and The Register. Some websites suggest that some common inaccuracies in Microsoft's figures stem from including figures for Unix and Solaris with figures for Linux. Individual Linux and Unix administrators may have higher salaries than Windows administrators, but they tend to be more efficient and thus able to handle more servers.

In 2004, the Advertising Standards Authority (ASA) of the UK warned Microsoft that an ad from the campaign which claimed that "Linux was ... 10 times more expensive than Windows Server 2003", was "misleading", as the hardware chosen for the Linux server was needlessly expensive. The ASA's complaint was that "the measurements for Linux were performed on an IBM zSeries [mainframe], which was more expensive and did not perform as well as other IBM series." The comparison was to Windows Server 2003 running on two 900 MHz CPUs.

In spite of the fact that Microsoft offers bundles of licenses for larger number of users, the cost variances are still heavily in favor of a RHEL deployment.

Don't even get me started on cost comparisons between the costs for a RHEL mail server vs. MS Exchange...