From this article:
“There’s no reason whatsoever why the Intel architecture remains so complex,” said Simon Crosby, chief technology officer at virtualization software start-up XenSource. “There’s no reason why they couldn’t ditch 60 percent of the transistors on the chip, most of which are for legacy modes.”
If a chipmaker declared its chip could run only software written past some date such as 1990 or 1995, you would see a dramatic decrease in cost and power consumption, Crosby said. The problem is that deep inside Windows is code taken from the MS-DOS operating system of the early 1980s, and that code looks for certain instructions when it boots.
To maintain backward compatiblity with Windows, chip manufacturers still have ancient x86 code which adds processing overheads to the current generation of processors. Time to have an open source processor, fully optimised for Linux with no legacy code.