The drive is a standard, off-the-shelf Seagate Barracuda drive. We're cheapskates (hey, you never know when you might kill a $3,000 Retina MBP while trying to open it), so we opted for the 2TB option.

The standard SATA drive has a not-so-standard, super-thin connector that attaches it to the mothership motherboard.

The SATA cable's super-thin profile allows the hard drive to be plugged in, as well as allowing it to be clamped securely into the enclosure via the rubber cover (and metal clamp).