Saving Data When Turned Off

[Carl Fredrik Ahl]

Hi,

I have a Garmin Instinct watch. When I press one of the buttons I come to a place where I can choose to set alarm, timer, stop watch etc. It will remember what I did last and show that when I get to the that place again. For example, if I use the alarm, the alarm will be displayed first. How does the watch save this even when it's turned off? It can't stay in RAM if the watch is turned off right?

[Sensei]

It's stored on some kind of non-volatile memory

https://en.wikipedia.org/wiki/Non-volatile_memory

e.g. Arduino has RTC module. You can read current time of real-time clock (RTC), write it, but can also read and write NVM which is on it. It's not much, just 56 bytes. (the rest (8 bytes) are used by time & date).

 

Edited June 11, 2019 by Sensei

[Christopher]

I don't know the internals of that part but some processors have a hibernate mode where some tiny amount of energy maintains the memory, even for years on a tiny battery.

[StringJunky]

13 minutes ago, Christopher said:

I don't know the internals of that part but some processors have a hibernate mode where some tiny amount of energy maintains the memory, even for years on a tiny battery.

You're probably thinking of the cmos battery.

[MigL]

Some 'flash' memory will be retained for quite a while ( decades ); even without battery back-up.
( think USB storage sticks  or SSDs )