SSD固态硬盘接口 M2

高传输速率的要求，SATA接口的硬盘，替代了IDE接口的硬盘。

随着便携式电脑小体积的要求，intel又设计提出了M.2接口。

M.2接口有2中物理接口形式：socket2和socket3，B-key (Socket 2) and M-key (Socket 3).

Socket 2支持SATA和PCI-E 3.0×2通道，采用AHCI协议类型，简单来说就是这类M.2固态硬盘与SATA接口的固态硬盘的传输速率相差微乎其微，最大标定传输速率不会过千兆。

Socket 3则采用NVMe协议，接口样式略有不同，传输速率最低也可达到千兆以上，有NVMe协议取代AHCI协议的趋势。

目前固态硬盘闪存颗粒的密度，大致可按照SLC＜MLC＜TLC＜QLC理解。

密度越大储存性能越好但与之相反的是寿命越短。

而SLC虽然寿命较长，但由于颗粒密度小在传输速率和性能方面体验较差。

SATA (Serial Advanced Technology Attachment) interface.

The current popular version is SATA Revision 3.0 (so-called SATA 6Gbps), which was published by Serial ATA International Organization (SATA-IO) in .

SATA interface mainly uses AHCI (Advanced Host Controller Interface) protocol.

NVMe(Non-Volatile Memory express) protocol is first published in . Compared with AHCI, it can reduce latency time greatly owing to no need for accessing register when giving a command.

The Mini-SATA (mSATA) interface, though designed specifically to provide the smallest form factor for SSDs, is limited by the SATA 6 Gb/s link.

M.2 was originally called the Next Generation Form Factor (NGFF), and then formally renamed to M.2 in . M.2 improves on the mSATA standard, which uses the PCI Express®Mini Card physical card layout and connectors. As mSATA's "successor," M.2 provides higher performance and capacity while minimizing module footprint.

参考：/blog/what-is-m.2-M-B-BM-key-socket-3