Apple's latest 15-inch MacBook Pro | Source: iFixit
The 13-inch version of Apple's latest Retina MacBook Pro lineup benefited the most from Haswell's focus on power efficiency, reducing the number of fans in the clamshell casing from two to one, according to iFixit. The reduction is likely one of the primary reasons Apple was able to shrink the smaller laptop's vertical cross-section to match its larger sibling's 0.71 inch thin profile.
The new 13-inch Retina MacBook Pro featuring a single-fan design | Source: iFixit
Both the 13- and 15-inch variants sport a new, streamlined heatsink which combines the thermal pads for the CPU and GPU. Previously, each chip -?in models with discrete GPUs --?had its own thermal pad, and the two were connected to the fans via heat pipes.
An updated heatsink design featuring a single thermal pad for both the CPU and GPU | Source: iFixit
The repair site also noted that the headphone jack is now soldered directly onto the logic board, rather than connected via a ribbon cable or wire. Since the headphone jack is one of the few parts in the laptops that is subjected to repeated wear and tension, it makes replacing the port expensive.
New PCI-e based flash storage for the Retina MacBook Pro lineup | Source: iFixit
In addition to the structural changes, both units feature faster PCIe-based storage, which comes in the form of a replaceable daughtercard. The laptops' other elements, including the display construction and battery placement, remain largely the same.