原创 注意对NVRAM的两种理解

通常NVRAM被等同于NVM，称为非易失性存储器。通俗地说，掉电不丢失数据的存储器都可以称为NVRAM，诸如EPROM、EEPROM、FLASH、FRAM（铁电存储器）等。因此NVRAM并非指某一种存储器的制造工艺，而是一种功能上的分类。

但必须注意的是，NVRAM有时还可专门指一种掉电数据保护的SRAM器件，原理大致是“SRAM+电池”，掉电以后，SRAM自动使用片内的电池供电，以达到保护数据的目的，如下图。其实质是一种组合模块，并非是一种新的半导体工艺。

查看ST公司的网站即可发现有一种器件被称为NVRAM的，与EEPROM、FLASH等器件并列，可见这里是一种专称，初次接触者很容易搞混淆。

下面是摘抄的一种定义，可供参考：

NVRAM: Non-Volatile RAM. The target is to have a electrical device that could be accessed quite fast, most of the time the content is calculated by bytes and the content could be saved after power down. There are different technical ways to implement this concept such as EEPROM which is very common. Please note, in mobile phone design, most of the time one or two sectors of ROM (most of the time it is FLASH) will be used to simulate NVRAM, the only reason is cost saving since ROM is a "must" but NVRAM is not.

FLASH: One kind of ROM and the difference to other ROM is semiconductor level. Please note, FLASH must be read/write by sectors but NVRAM should be read/write by bytes. It is why NVRAM driver have to implement an algorithm such as copying all the content in one sector to RAM first.

NVM: Non-volatie memory. It is more generic concept and covers all the memory components that could keeps its content after power off. It is useful during architecture design when the technical detail could be skipped. In fact, in one project, a DRAM with battery played as NVM and it worked quite good in that case.
本文来自：我爱研发网(52RD.com) 详细出处：http://www.52rd.com/bbs/printpage.asp?BoardID=67&ID=28678