Imagine if there was a resurgence of mainframes. IBM says they are greener than Unix and PC servers, and the savings in electricity are substantial. Could environmental savvy IT directors migrate applications onto the mainframe to lower their data centre electricity bills.
The mainframe is based on virtualisation technology that has evolved over the last 40 years, which makes it a great platform to run and manage virtual machines. IBM even sells IPL, an add-on processor dedicated to running Linux applications. A single mainframe can run hundreds of Linux virtual machines.
The green mainframe argument simply states that it is possible to replace hundreds of physical Linux-based PC servers with a single mainframe. The total electricity and cooling costs of running the Linux PC farm is far greater than if the same software environment was ported to the mainframe and run as virtual Linux machines.
This may have made sense a couple of years ago. However, thanks to VMWare, PC server virtualisation is mainstream. IT departments can run many copies of Linux (or Windows) on the same physical hardware. So if the green sums are calculated now, is the mainframe really greener compared to a modern (ie green) PC server running multiple copies of Linux on top of VMWaare or Xen?