存储设备/接口/传输协议总结

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1. 设备

最新的3D XPoint存储器比DRAM慢10倍，便宜2倍；比NAND FLASH快1000倍，贵5倍左右，性能比其他PCIe和NVMe的SSD快10倍左右。并且它是一种NVM。

下表摘自[2]

Type	Volatile?	Writeable?	Erase Size	Max Erase Cycles	Cost (per Byte)	Speed
SRAM	Yes	Yes	Byte	Unlimited	Expensive	Fast
DRAM	Yes	Yes	Byte	Unlimited	Moderate	Moderate
Masked ROM	No	No	n/a	n/a	Inexpensive	Fast
PROM	No	Once, with a device programmer	n/a	n/a	Moderate	Fast
EPROM	No	Yes, with a device programmer	Entire Chip	Limited (consult datasheet)	Moderate	Fast
EEPROM	No	Yes	Byte	Limited (consult datasheet)	Expensive	Fast to read, slow to erase/write
Flash	No	Yes	Sector	Limited (consult datasheet)	Moderate	Fast to read, slow to erase/write
NVRAM	No	Yes	Byte	Unlimited	Expensive (SRAM + battery)	Fast

2. 接口

2.1 分类和发展

(P)ATA(Parallel AT Attachment)/IDE(Integrated Drive Electronics) --> SATA(Serial ATA) --> mSATA(mini-SATA) --> SATAe(SATA Express)

SCSI(Small Computer System Interface) --> SAS(Serial Attached SCSI)

PCIe

NGFF(Next Generation Form Factor, M.2)

mSATA / PCIe / NGFF 一般都是用于NVM(如SSD)，不用于HDD。
mSATA慢于SATA，但是接口和体积大大减小。
NGFF是最新的，同时比mSATA更小，也是最快的。
SATAe接口兼容SATA和PCIe

2.2 速度：

NGFF > PCIe > SAS > SATA > SCSI > ATA/IDE

3. 协议

IDE, AHCI和NVMe等都是传输协议，它们在传输接口(PCIe, SATA, ATA等)之上工作。

IDE(Integrated Drive Electronics)是IDE接口的一种“协议”，它表示磁盘控制器集成到了硬件驱动器中，无需host进行移动磁道臂等低层次的控制。
AHCI(Advanced Host Controller Interface)一般用作SATA盘的协议，不过也有些情况SATA盘用IDE协议(老版本的Windows中默认的IDE/legacy模式就是这样)来模拟。
SAS的协议向下兼容SATA盘。
NVMe支持PCIe接口或者NGFF接口的盘。

参考

[1] Breakthroughs in Memory Technology, http://www.intelsalestraining.com/memorytimeline/

[2] Types of Memory in Embedded Systems, https://barrgroup.com/Embedded-Systems/How-To/Memory-Types-RAM-ROM-Flash

[3] What’s the difference between SATA, PCIe and NVMe?, http://www.userbenchmark.com/Faq/What-s-the-difference-between-SATA-PCIe-and-NVMe/105

[4] https://www.intel.com/nvm

[5] Hard disk drive interface, Wikipedia, https://en.wikipedia.org/wiki/Hard_disk_drive_interface

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