FLASH, NVM 和 nvram 区别

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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.  

Benefits of NVRAM
NVRAM chips work like static RAM
NVRAMs provide superior performance over other NVM products
NVRAM's serve applications that require high-speed read/write operations with non-volatile memories such as parallel processing controllers for LANs and antilock braking systems.
NVRAM chips don't require much power and backup can be guaranteed for up to ten years.
Bad NVRAM
When NVRAM is failing, it generally means that your computer hardware is not retaining the necessary specialized settings that it ought to though the default BIOS settings remain. Since the BIOS relies on the settings stored in NVRAM in order to handle the particular hardware you have, performance may lack in stability. The contents of the NVRAM chip can become corrupted for a variety of reasons:
A failure of the embedded battery. If the battery embedded in the NVRAM chip fails, then this means that your system clock will stop running and important system configuration information may not be maintained.
A failure of the CMOS (BIOS) chip on your motherboard. If the CMOS chip is going bad or is not making proper contact with the motherboard's contacts, then the NVRAM will fail.
When you get an error message about your NVRAM:
You may need to purchase a new CMOS battery at your computer store to replace your current one. It is advisable to have a technician observe the battery first and determine whether you really need a new one.
If the BIOS chip was the problem, then you will need to contact your hardware manufacturer who may give you a replacement chip depending on your warranty. If not, then you will need to replace your motherboard.
You could also try to reprogram the NVRAM chip with a hostid and ethernet address. You should only attempt to do this if you know exactly what you are doing; otherwise you should seek a technician's guidance.


本文来自ChinaUnix博客，如果查看原文请点：http://blog.chinaunix.net/u1/54388/showart_1833032.html