Improved by Haswell. A notebook that you carry around all the time should be as light as possible, but also sturdy and enduring at the same time. Lenovo tries to meet these requirements with the ultrabooks of the ThinkPad S-series. We review the ThinkPad S540, the current 15.6-inch model from the series. The biggest improvement: The S540 models are equipped with Haswell processors.
http://www.notebookcheck.net/Review-Lenovo-ThinkPad-S540-20B30059GE-Ultrabook.111259.0.html