The bottom mini PCIe slot accommodates half height cards (for WiFi, presumably) and you can go ahead and put an mSATA drive or full height card at the top.

ENGADGET: Intel's NUC mini-PC internals exposed, available for around $300 in early December

Expansion is limited to a pair of DDR3 SO-DIMM slots (16GB max), one full-size mini PCIe slot that supports mSATA SSD drives and one half-size mini PCIe slot that's perfect for WiFi and Bluetooth.

ENGADGET: Intel NUC review: a little desktop PC that holds big promise

As we saw in our IDF hands-on, the NUC holds a Core i3 CPU, HD 4000 graphics, two SoDIMM sockets, mSATA and mini-PCIe interfaces, one to two HDMI and three USB 2.0 connectors.

ENGADGET: Intel's NUC mini-PC internals exposed, available for around $300 in early December