CES 2014 -Seagate displayed it's new 5mm HDD's that stick with the standard SATA connection. For a complete view of the performance capabilities of the drive feel free to take a look at the Seagate Laptop Ultrathin HDD Review by our very own Tyler Bernath.
To give some perspective, I took a snap of the HDD next to my Samsung Galaxy Note 3. This thin profile allows this HDD to be deployed into just about any thin device.
The thin HDD's from Seagate's competitors feature a new edge connector, which hasn't made much headway in terms of mass adoption. The slow uptake, or lack thereof, of the edge connector has led Seagate to forgo use of the spec, since it is much more financially viable for companies to use existing standards at this point. Of course that could be subject to change in the future as devices shrink, but selling relevant products for today's market is Seagate's focus.