M.2

M.2, formerly known as the Next Generation Form Factor (NGFF), is a specification for internally mounted computer expansion cards and associated connectors. It replaces the mSATA standard, which uses the PCI Express Mini Card physical card layout and connectors. M.2 can run an SSD over SATA (different than mSATA) or PCIe. The difference between M.2 SATA and M.2 PCIe can be discerned by their key notches. SATA M.2 cards (not to be confused with mSATA, which has two connector keys) have three connector notches while PCIe M.2 cards have only two. M.2's more flexible physical specification allows different module widths and lengths, and, paired with the availability of more advanced interfacing features, makes the M.2 more suitable than mSATA for solid-state storage applications in general and particularly for the use in small devices such as ultrabooks or tablets. Computer bus interfaces provided through the M.2 connector are PCI Express 3.0 (up to four lanes), Serial ATA 3.0, and USB 3.0 (a single logical port for each of the latter two). It is up to the manufacturer of the M.2 host or device to select which interfaces are to be supported, depending on the desired level of host support and device type. The connector keying notches of M.2 devices denote various purposes and capabilities of M.2 hosts and modules. The unique key notches of M.2 standard cards and devices also prevent them from being inserted into incompatible host connectors. In addition to supporting legacy Advanced Host Controller Interface (AHCI) at the logical interface level, M.2 specification also supports NVM Express (NVMe) as the logical device interface for M.2 PCI Express SSDs. While the support for AHCI ensures software-level backward compatibility with legacy SATA devices and legacy operating systems, NVM Express is designed fully to utilize the capability of high-speed PCI Express storage devices to perform many I/O operations in parallel.:14 Buses exposed through the M.2 connector are PCI Express 3.0, Serial ATA (SATA) 3.0 and USB 3.0, which is backward compatible with USB 2.0. As a result, M.2 modules can integrate multiple functions, including the following device classes: Wi-Fi, Bluetooth, satellite navigation, near field communication (NFC), digital radio, WiGig, wireless WAN (WWAN), and solid-state drives (SSDs). The SATA revision 3.2 specification, in its gold revision as of August 2013, standardizes the M.2 as a new format for storage devices and specifies its hardware layout.:12 The M.2 specification provides up to four PCI Express lanes and one logical SATA 3.0 (6 Gbit/s) port, and exposes them through the same connector so both PCI Express and SATA storage devices may exist in the form of M.2 modules. Exposed PCI Express lanes provide a pure PCI Express connection between the host and storage device, with no additional layers of bus abstraction. PCI-SIG M.2 specification, in its revision 1.0 as of December 2013, provides detailed M.2 specifications.:12 Three options are available for the logical device interfaces and command sets used for interfacing with M.2 storage devices, which may be used depending on the type of M.2 storage device and available operating system support::14 The M.2 standard has been designed as a revision and improvement to the mSATA standard, with the possibility of larger printed circuit boards (PCBs) as one of its primary incentives. While the mSATA took advantage of the existing PCI Express Mini Card (Mini PCIe) form factor and connector, M.2 has been designed from the ground up to maximize usage of the PCB space while minimizing the module footprint. As the result of the M.2 standard allowing longer modules and double-sided component population, M.2 SSD devices can provide larger storage capacities and can also double the storage capacity within the footprints of mSATA devices.:20,22–23