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 2009.
SATA interface mainly uses AHCI (Advanced Host Controller Interface) protocol.
NVMe (Non-Volatile Memory express) protocol is first published in 2011. 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 2013. 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：https://www.atpinc.com/blog/what-is-m.2-M-B-BM-key-socket-3