NAND

1）  SMART: 自我检测分析和报告技术（Self-Monitoring Analysis and Reporting Technology）成为一种自动监控硬盘驱动器完好状况和报告潜在问题的技术标准。

Volatile memory = Volatile Storage 易失性存储器/非永久性存储器

Volatile memory loses data when power is removed from the device.掉电丢失数据。DRAM

Non-Volatile memory maintains the data without power.非易失性存储器，掉电不丢失数据。

Flash Memory（NOR Flash和NAND Flash）

2）  NOR Flash特点

--  Random access - Think of accessing a page in a book访问书中的某一页

--  Long erase and write time 擦除和写的时间长

--  Ideal for program code storage 适合存储程序代码（容量小，代码一般都小）

--  No intrinsic bad block management. 没有固有的坏块管理

3）  NAND Flash特点

--  Sequential access – Think of accessing a song on a cassette tape 磁带

--  Faster write and erase time

--  Higher density/Lower cost 高密度/低成本

--  Ideal for large amounts of data storage 适合存储大量的数据（容量大）

--  Requires bad block management 需要/要求对坏块进行管理

Stores data by Page and erase in Blocks / Cheap and no high density limitation

NCQ命令：device端的命令未处理完（没有报告命令已处理完），host端可以再发其它的命令。而device端可以不按顺序执行命令。

非NCQ命令：必须等待NCQ命令的32个slot中的所有命令完了之后。

------ Why do we use NAND instead of NOR if it’s slower?

It’s cheaper and good enough.

4）  Software for NAND?

-----Unlike DRAM, NAND Flash needs a NAND controller or software

-- DRAM: The processor is allowed to write a 1 or a 0 to any bit

-- NAND: Flash bits can only be "written" from 1 to 0. Erase operation / Needs software or smart controller.

-- Software may be required in embedded applications, used to manage the NAND device if a "dumb"controller is used. Software job duties include:

----- NAND Flash data management 数据管理

----- Bad Block Management 坏块管理

----- Wear Leveling of NAND flash blocks 块的磨损程度/级别

5）Controller for NAND

-- Controller manage the NAND device to provide a simple, accurate data flow.

-- Bad block management / Bit flipping 比特翻转/Error correction/Wear leveling

A controller can provide one interface to many NAND chips to simplify the customers design.

6）EMMC （Managed NAND）

-- eMMC：embedded Multi-Media Card内嵌式多媒体卡

eMMC的一个明显优势是在封装中集成了一个控制器，它提供标准接口并管理闪存，使得手机厂商就能专注于产品开发的其他部分，并缩短向市场推出产品的时间。

ECC：Error Correction Code纠错码  MMC：Multi-Media Card多媒体卡

OEM：Original equipment Manufacturer原始设备制造商

slot：位置，插槽 expansion slot扩展槽

7）What is ONFI

--ONFI: Open NAND Flash Interface 开放式NAND闪存接口 Includes NAND vendors（供应商）,enablers

（推动者）and customers. Purpose is to standardize the NAND Flash interface.

8）SSD and HDD

--SSD：Solid State Disk固态硬盘enclosure not required

Disassembled (拆散了的，拆开的)SSD is more like a memory module with multiple NAND devices and a controller. No moving parts.

Power Consumption:No moving parts = less power consumption = more battery life

--HDD：Hard Disk Drive硬盘驱动器，硬盘驱动器简称硬盘，一种主要的电脑存储媒介。

早期台式电脑使用的硬盘采用IDE接口，(Integrated Drive Electronics)电子集成驱动器

指把“硬盘控制器”与“盘体”集成在一起的硬盘驱动器。

Disassembled traditional HDD showing the many mechanical moving parts.

9) Key Terms

ATA: Advanced technology attachment.先进技术附件，并行接口。

Hard drive interface standard标准硬盘接口

Hot Swap: 热交换，热插拔，A hot swap is the replacement of a hard drive, CD-ROM drive, Power Supply or other device with a similar device while the computer system using it remains in operation.

Plug and Play:即插即用，A computer feature that allows the addition of a new device, normally a peripheral, without requiring reconfiguration or manual installation of device drivers.

EDS：Electronic data storage电子数据存储 is storage which requires electrical power to store and retrieve that data.

AFR: Annual Failure Rate,年度失败率 - The relation between the mean time between failure and the assumed hours that a device is run per year, expressed in percent. 失败的时间 as compared to MTBF (Mean time between failures)平均故障时间- is a measure of how reliable aproduct is (time between failures due to manufacturing or component defects) Usually given in units of hours, the higher the MTBF the more reliable the product is.

Form Factor：形状系数，the physical sizeand shape of a device.

RAID: Redundant Array of Independent Disks. A group of SSDs or HDDs that operate together to improve performanceor provide fault tolerance(容错) and error recovery through data striping（数据分割）, mirroring and other techniques. RAID can be accomplished(完成) in a system via hardware (controller) or software.

SAS: Serial Attach SCSI(Small Computer System Interface,小型计算机系统接口),串行连接，Point - to– point Serial protocol transfer technology designed to replace the parallel bus technology of SCSI. Compatible with SATA drives for reduced complexity in the data center. Hot swappable。

SATA：Serial Advanced Technology Attachment. The latest interface used for connecting storage devices inside PCs. Hot swappable.

Latency: The time it takes the HDD to rotate to the position where the data on the track(磁道) are aligned below the read/write head.

Fibre Channel :光纤通道/光纤信道，A high speed interconnect used in storage area networks(SAN,存储区域网) to connect servers to shared storage via a serial data channel over fiber optic cabling. Fibre channel hardware interconnects storage devices with servers and forms the fibre channel fabric(构造，组织).

The fabric consistsof the physical layer (cables that carry signals),interconnect devices (hubs, switches),and translation devices (host bus adaptors).

PCIe: Peripheral Component Interconnect Express外围部件互连，a computer expansion card interface designed to replace the general – purpose PCI Expansion bus, the high-end PCI-X bus and the AGP graphics card interface. Unlike previous PC expansion interfaces, rather than being a bus it is structured around point-to-point serial links called lanes.

IOPS: Inputs/Outputs per second – is a standard benchmark (computing) provided by applications such as IOMeter, IOZone and FIO. It is primarily used with servers to determine their best configuration settings. The specific number of IOPS possible in any server configuration will vary greatly depending upon the variables the tester enters into the program, including the balance of read and write operations, the simulated randomness of the data, the number of worker threads and queue length, as well as the data block sizes. 

Because of this, published IOPS are often misleading （令人误解的）and generally represent the best case scenario（最佳设计方案）.