Is M.2 the prince of SSD form factors?

In my translation of an article on SSD form factors, I talked about how various solutions evolved in the field of solid-state disks. In short, the M.2 format was also touched upon, which in fact deserves a closer look. Recently, the second part of the article, which sheds light on this issue, appeared on LSI's blog. I bring to your attention its translation.

Story

A few years ago, the non-profit organization PCI Special Interest Group (PCI-SIG), in partnership with The Serial ATA International Organization (SATA-IO), began developing a standard combining the ideas of Mini-PCIe and mSATA, these two standards were intended to replace the innovative M.2 . The new board and connector should have been used for a variety of peripherals, WiFi, WWAN, PCIe, GPS, NFC and SATA with SSD supporting both PCIe and SATA interfaces. The groups set out to create a narrower connector offering higher speeds, a small card thickness, and variable length expansion cards to support very small computers and laptops.
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The new format also had to support micro-servers and similar high-density systems, allowing dozens of M.2 cards to be installed. Unique connector cuts, also called “keys,” should help distinguish between a wide range of products that use the M.2 connector and protect against connecting incompatible devices into unsuitable connectors.

Rename

Initially, the form factor M.2 was supposed to be called “Next Generation Form Factor” (Next Generation Form Factor or abbreviated NGFF). At this time, the PCI SIG was already developing a specification that bore such an abbreviation, therefore, in order to avoid confusion, the new development was renamed M.2. The name did not catch on quickly, so in many articles these solutions are called “M.2, formerly known as NGFF”.

Keys

In the world of connectors and sockets, “keys” help to avoid connecting incompatible equipment, as well as to protect against incorrect connection (for example, the wrong side). Specification M.2 defines 11 key configurations, 7 of which are reserved for future use. Jacks should always have one key lip, while expansion cards can have multiple key cuts if they are compatible with several different jacks at the same time. Of the 4 keys currently involved, 2 are used for SSDs. The key with identifier B (pins 12–19) gives the PCIe SSD up to two data lines, and the key with identifier M (pins 59–66) gives four lines. Both options can also support SATA devices. All key placement options are unique, so connecting the card upside down will not work.



Unfortunately, the keys alone are not enough to inform the user enough about the SSD and help to choose the right device to upgrade / replace. For example, a computer with an M.2 socket for PCIe x2 uses a B key, which prevents you from connecting a card with PCIe x4 (M key). But at the same time, the SATA M.2 card with the B key can be safely connected, despite the fact that the computer does not recognize the SATA commands that come through the PCIe M.2 socket. Because of this incompatibility of signals, users need to carefully study additional data that is either printed on the socket or indicated in the instructions in order to understand whether the socket is a SATA or PCIe.

Length and height

The pins of connector M.2 are distinguished by a higher density than previous standards. This allows you to make a fee already, and, therefore, opens the way for thinner and lighter mobile computers. Moreover, the M.2 specification describes modules with components located only on one side of the board, leaving enough space for other components between the motherboard and the expansion card itself. The number of flash memory chips used by the SSD varies depending on the capacity of the drive, so for smaller disks you can make shorter boards, leaving enough space for other components of the mobile system.



What's in your name

When I hear people call this specification “M.2, formerly known as NGFF”, I involuntarily recall the story of the musician Prince, who changed his own nickname to an unpredictable character, and everyone had to call him “an artist, formerly known as Prince ". In that case, I think it was done for the sake of unnecessary PR buzz.

In the case of renaming NGFF to M.2, I doubt that the goal was the same. In fact, I am sure that the main idea of ​​renaming was to simplify branding by removing the second name for the same specification. Although it doesn’t matter what we call this new form factor, it’s designed to thrive in mobile computers and the high-density server market.