The latter board included SO-DIMM (small outline dual in-line memory ... due to the large size of the LGA 2066 socket. It's not the only example of a desktop motherboard with SO-DIMM slots.

The most mainstream and common motherboard form factor ... 2" or SR-2 mobo), which was designed to accommodate dual QPI LGA 1366 socket CPUs and 12 DDR3 RAM slots.