When we now look at data and how it lives on the handset,
it's very important that you understand solid state flash
memory properties.
Now, you're going to see here, we
have this first 4-kilobyte chunk that is in blue.
Data is going to be written in these chunks.
And these are referred to as pages.
Now, as data comes into the device
or goes out of the device, that page
has to be moved all around the phone.
Otherwise, your device would wear out and die.
If you think about this, if data is constantly
being written to the same place, your phone
is going to wear out.
To prevent that, we have data that's
going to be moved around the phone.
Let's think about this.
If you send me a text message, there
is a database that exists on that Android or iPhone.
And that could be in that first blue chunk of information.
As it moves, if I respond to you,
it's going to move to a different location.
If you respond back to me, it's going
to move to a different location.
But what I want you to think about
is, you send me that one text message,
and I never respond to you.
Not only do I not respond--
I ignore it.
But then I start texting my dad.
I text my brother and my friends.
Every time I'm accessing that database,
that data moves around.
Now, what's really important is, I
realize you should have never texted me
and I delete it to cover our tracks.
Every time that database moved around,
it could exist in another chunk on this data set.
On that device, all of these chunks that are moved around
are not erased until the entire block is ready,
meaning each of these pages are marked as no longer needed,
please delete me.
That entire data will be erased in blocks.
This is what we are going to talk about with wear leveling.
Wear leveling is not going to exist on all devices.
But understanding how the data exists on the actual device
is important with understanding why you may uncover things
that the user thought they had previously deleted.