Cloud computing for the most part runs on AMD and Intel commodity servers running the operating systems most common to Intel's x86 instruction set, the basis for its Xeon family and other chips. Consequently, it's possible to conclude that Windows Server and Linux are the operating systems that will dominate cloud computing for the foreseeable future. But there are a few exceptions, and one of them may catch on as an alternative.
HP is producing data center servers based on Calxeda-designed ARM chips for telecommunications firms and other customers that remain unnamed. ARM doesn't run x86 applications, but it is an energy-conserving architecture originally designed to power mobile devices. At six watts per core, versus 80-100 watts in the typical Intel server today, an ARM-based data center with hundreds of thousands of servers would save significant energy -- while also not being able to run a significant amount of software created for the x86 server world. HP is experimenting with another low-wattage server for the future data center, based on Intel's Atom chip. It uses only seven watts an hour and does run x86 software.
Then there's the example of Joyent infrastructure-as-a-service (IaaS) running its SmartOS operating system, a derivative of open source Illumos. The Illumos project was started to create an alternative provider of Solaris, which became open source code itself in June 2005. In eyes of critics, Solaris ceased to exist as an open system with the release of Solaris 11 by Oracle in November 2011. Oracle had acquired Sun and brought the operating system back in house over the intervening two years. Illumos, meant to suggest "illuminate" from its Latin root, was created by OpenSolaris advocates in 2011 as they saw the writing on the wall. Joyent's SmartOS version is expected to become more generally available for on-premises and private cloud use next year, according to company officials.
So will ARM or SmartOS replace the predominant Windows and Linux? Not anytime soon. But ARM offers big power savings advantages for the cloud, while SmartOS offers advanced reliability and self-healing advantages. Neither system should be counted out.