OS X Mavericks has bunches of improvements under the hood that Apple says will improve your MacBook's CPU performance by up to 72 percent. More power and better battery life, designed for users on that go.
How does the new OS improve CPU performance so much? First up, it's a technology called Time Coalescing, which smooths out the curve of CPU usage so that rather than alternating between passive and active states it's more smoothly transitioning.
Apple has also added improvements to Sarafi that make it way more efficient than Chrome and Firefox. A technology called "App Nap" helps the OS focus exactly on what app you're using so that you're not burning up battery life in the background.
This all sounds great, but we'll have to see how it performs in real life.