[NTLK] flash longevity question

Victor Rehorst victor at chuma.org
Thu Sep 15 14:13:38 PDT 2022

On 2022-09-14 20:21, Dan wrote:
> Wow Victor!  Thank you!  I knew that the chips were NOR but I have heard the phrases used interchangeably with NAND.  A large mistake as they are very different.  I suspected as much but couldn't find the details when I looked.  Apparently I was using the wrong search terms.
Hey, no problem, it was a fun exercise for a Tuesday evening for me :)
> I did have a hunch the older, less dense chips would be a world of difference with regard to longevity.  What IS fascinating to me is the large push for the flash drives when there is a obvious longevity problem, and no one talks about this.  Sure for the moment it is fine and if you are using it not for long term storage no problem.  But consider how many devices have these chips in them which most people think 'flash is forever' if it is just sitting there which is not the case.

Longevity is relative, and let's face it: the vast majority of consumer 
electronics are made to be disposable, not durable.  When it comes to 
NAND vs NOR, they have different use cases in computing.  NOR flash is 
meant to be a flexible replacement for mask ROM; both are 
byte-addressable, which means code can be executed directly from it, 
instead of being copied to RAM first. NAND flash is a replacement for 
hard disks: large capacity, and block-addressable.

In terms of preservation, best practices for flash memory seem to boil 
down to:

1. Keep program/erase cycles as low as possible.
2. Don't store at extremely hot temperatures.
3. Power on every now and then, to refresh the charge in the flash.


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