IBM is replacing servers in its own datacentres with 30 mainframes to save energy. It also gives the company a chance to show that the mainframe is still alive.

IBM, in the first action since announcing Project Big Green in May, said that it expects to reduce its energy bill by 80 percent, and save $250 million in overall costs, by replacing the 3,900 servers with its System z mainframes running Linux.

Servers operate at anywhere from 10 to 20 percent of capacity because they usually run only one software application. But mainframes operate at an average 80 percent of capacity meaning one mainframe can replace multiple servers, said Bernie Meyerson, an IBM fellow, vice president of strategic alliances, and chief technologist. And virtualisation, the process of dividing a server into multiple logical servers to improve utilisation, was pioneered on mainframes decades ago, he said.

If 30 mainframes can do the work of 3,900 servers, any company can reduce their server count and reduce the need to build more datacentre space, which is challenging given tight energy supplies, Meyerson said.

"In major metropolitan centres there ain't another electron available," he said. "[A mainframe] eliminates the need to build more datacentres and build power plants to feed them."

IBM's mainframe project will bring some attention to the platform and prompt some IT customers to reconsider using them, said Mike Kahn, managing director of The Clipper Group, a research firm.

"A lot of people can't imagine that the dinosaur still has the economic advantages to deliver that," Kahn said, of the mainframe's estimated energy savings.

The IBM mainframe also has a cost advantage over servers in that it features specialty processors that IBM developed to work in an open Linux environment, he said. Standard x86 processors are relatively costly because they run legacy applications in an IT system. But speciality processors developed by IBM for mainframes running Linux are less expensive. These speciality processors include the Integrated Facility for Linux (IFL), a processor called Zip, which runs Java applications on a mainframe and Zap, which runs DB2 applications.

While IBM's project will draw new attention to the mainframe, they are not for everyone, said Charles King, an analyst with Pund-IT Research. Users chose servers over mainframes because they were more affordable, he said.

"The distributed server environment put a tremendous amount of computing power in the hands of users for much less money," King said.

HP is in the midst of its own datacentre consolidation project, reducing to six the number of datacentres it operates, from 85.