Assuming a modern SSD/Phone. If the hardware doesn’t physically change and I can’t open it and see 1’s and 0’s, then how does the device know the state before the electricity went off?
In: Technology
> Assuming a modern SSD
We need to talk about how an SSD physically works. There are billions of tiny microscopic “islands” inside surrounded by insulators. When writing data, an SSD uses a high voltage electric field to forcibly blow (suck) electrons onto (off of) the islands.
If there’s no charge it’s a 0 bit, if there’s charge it’s a 1 bit.
Once on the islands, the electrons are trapped and stay there for decades, or until you decide to write something else with another high voltage electric field.
When you want to read data, the trapped electrons have an electric field of their own. So you can use an electric field detection circuit to tell whether each island has charge or not, which gives you your the 1’s and 0’s back.
> If the hardware doesn’t physically change
It does physically change. Electrons are physically moved into different positions depending on what data you write.
Imagine that you have an row of switches [like this one](https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSnYaNe0JTAf7vBYc0xr_v9639nr3eBvVStffCfdURBeYdbuj2H5YTWYuvcg2xsElw1gPM&usqp=CAU), that you can turn on or off, and to “write” information, you put them in different positions. Those switches need energy (your fingers) only when you want to change them, but if there’s no energy they get stuck in their state.
At the lower level, the methods of storing data you mentioned need energy to change their state (i.e. writing), but not to keep it, being a disc that is magnetized at different parts (as in a typical HDD), a chemical dye that is heated to change its shape (as in a CD-RW), or little “switches” (as in a flash drive).
At its most basic level, an SSD is a grid of capacitors. That grid stores information by being in a charged state or an uncharged state (1s and 0s as you mention)
Similar to a traditional harddrive, the capacitors are given a location by the cpu bridge, and when it needs to read state, it simply reads out the capacitance.
This is also the reason that SSDs typically last longer if they aren’t used for continuous rewrites.
Its the same thing as any other file on an ssd(in a phones case) it is imprinted as 0s and 1s on the ssd memory chips and is read as the picture. This does not go away or change with the removal of power
ELI5 answer.
The hardware actually does physically change. When a picture is saved to memory, the phone does a “write” command to the drive. This means the data for picture is physically written on the drive. It no longer needs electricity to maintain the data.
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