MacBook – What are the six openings on the bottom of the MacBook Pro for

The big difference between the 2011 and non-Retina 2012 models (there are no 2013 models, as of May, 2013) is the move from Sandy Bridge to Ivy Bridge, along with updated discrete graphics in the 15" model.

The Ivy Bridge processors bring a bit more speed, but more importantly for the MBP, they're more power efficient. That equates to improved battery life over the 2011 models, which is probably the most noticeable difference for everyday usage.

Depending on the tasks and specific models of CPU, Ivy bridge will probably yield a 5-10% performance improvement.

The other big addition is USB 3, which is a nice thing to have if you want high-performance external storage without paying the high costs of Thunderbolt drives.

On my 2015 Macbook Pro, what looks like two ambient light sensors is actually a light sensor on the left of the webcam, and a green LED on the right of the webcam that lights up when Facetime is open to let you know the camera is in use.

The sensor on the left can be tested by waving a flashlight in front of it and observing the keyboard dimming. The light on the right can be verified by opening Facetime.