M.2 is interesting not just because it can speed up storage with PCI Express lanes, but because it can use a whole bunch of different buses too; it stands to replace both mSATA and mini PCI Express, two older standards that have been used for SSDs and Wi-Fi cards in laptops for a while now. Intel’s new Broadwell CPUs and their chipsets include native support for M.2 and PCI Express boot drivers—neither PCIe-connected storage (hi Apple) nor the M.2 connector itself are new, but beginning with Broadwell systems each of those two things will become much more common. - Understanding M.2

key / type

• A - Wi-Fi/Bluetooth, cellular cards
• B - SATA and PCIe x2 SSDs
• E - Wi-Fi/Bluetooth, cellular cards
• M - PCIe x4 SSDs

SSD type

not to be confonded with

• mSATA SSD interface