Difference of NVRAM and flash memory.

[maniac84]

Hi guys,

Just bump into NVRAM today. After finding some info on the net, NVRAM is a non-volatile RAM which means the user will still retain the data inside after power off. Then I'm wondering what is the difference of NVRAM and flash memory? Flash memory can also retain data after power off.

 

[FoxyRick]

Flash is one type of NVRAM; the term NVRAM does not in itself imply the use of any particular technology.

The other main NVRAM types at the moment are ferroelectric RAM (F-RAM) (which is a true non-volatile storage) and static RAM chips with built-in lithium cells to preserve data (like ST's zero-power memories, and many others).

No longer seen* types include core storage (truly random access and non-volatile) and bubble memory (truly non-volatile, but not really random access because it was sequential access albeit a lot faster than a tape!).

*At least, they aren't seen very often.

 

[thunderdantheman]

I have always grouped flash as a type of NVRAM, in there with EEPROM and... hmmm... that's all i can think of atm! Although it could be a bit grey around how 'randomly accesable' flash memory is...

 

[FoxyRick]

Flash is also a type of EEPROM.

One of the problems with all of this is that some of the terms themselves are not really logical, and different technologies with some different attributes have been 'bundled in' with existing acronyms. For instance, an old-fashioned EPROM is just as random access as static RAM, at least for writing, so could just as easily be called RAM. However, the term 'RAM' implies that the memory can be changed without resorting to bulk erasure.

The term EEPROM tends to be used for memory which is byte-erasable, as opposed to flash which is arranged to be block-erasable. Both can be considered random-access because locations can be individually addressed and read pretty much immediately, unlike a tape which is sequential access (so is a hard disk - but that is fast enough to also be called 'random access').

I'm a relatively old git now, so I've seen the changes in use of terms as new memory types are grouped in with older ones.