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I’m wondering generally what information is stored in an eeprom that’s different than what’s in the flash drive that contains firmware?

Mostly in mobile devices. Does the eeprom contain user settings like wallpaper, app locations etc or is there something else specific to hardware like IMEI etc?

Is the eeprom in a mobile phone comparable to bios in a pc or used differently?

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  • \$\begingroup\$ Which mobile device are you thinking of which has an EEPROM? Most store all persistent data in flash, but using file systems or block translation layers which distribute the wear by writing changed data to a different set of actual storage cells than that which it replaces. \$\endgroup\$ – Chris Stratton Nov 5 '17 at 16:24
  • \$\begingroup\$ Thinking more about iPhones. I read they have an anti-roll back eeprom and got me curious what information is stored on it. So user settings etc is stored in flash memory like the NAND? \$\endgroup\$ – user140123 Nov 5 '17 at 16:25
  • \$\begingroup\$ Usually, EEPROM's are very small and contain some type of hardware configuration data that can not easily be discovered by the bootloader or firmware (which both probably reside in flash, not EEPROM). For example, the EEPROM might contain information about what type of flash is present to make sure the bootloader can correctly read the flash. These are just general, speculative comments based on past experience. \$\endgroup\$ – mkeith Nov 5 '17 at 16:56
  • \$\begingroup\$ @mkeith Thanks your answer addresses the majority of my questions. However do you know where things like app layout, display settings etc would be stored? I know in tvs the eeprom has this info but is it different in a mobile device? \$\endgroup\$ – user140123 Nov 5 '17 at 17:31
  • \$\begingroup\$ I believe this varies quite a bit from system to system. \$\endgroup\$ – mkeith Nov 5 '17 at 18:02
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First, flash memory is a type of EEPROM (electrically erasable programmable read-only memory), so comparing them either/or doesn't make sense.

Second, there is no hard definition of "flash". It's more of a marketing term. It has converged to generally mean a type of EEPROM that is optimized for density, typically at the expense of slow write and erase times, and large erase blocks.

So given the above, flash memory is generally used for storage of large amounts of data. Those USB memory sticks hafe flash inside. In fact, they are sometimes called "flash drives".

In contrast, smaller EEPROMs that can erase and re-write individual bytes are often used for relatively (compared to a file system) small amounts of storage for things like configuration parameters, calibration coefficients, and the like.

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  • \$\begingroup\$ Why couldn’t the data stored in an EEPROM be stored in the flash memory along with firmware? And where are user settings stored? \$\endgroup\$ – user140123 Nov 5 '17 at 18:37
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    \$\begingroup\$ As a practical matter in industry EEPROM and flash are not the same. They are totally different categories of memory. I am sure you know this. \$\endgroup\$ – mkeith Nov 5 '17 at 19:04
  • \$\begingroup\$ @user: Sometimes there is no separate EEPROM and everything is stored in the larger flash. It depends on many parameters, including what the overall purpose of the system is, cost, reliability, etc. \$\endgroup\$ – Olin Lathrop Nov 5 '17 at 19:44

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