Where on my device could information be stored and deletion

[Nath_fiery]

Hello,

i have two smartphones. One Galaxy S7 and one Galaxy S8. The Galaxy S8 i use as my main smartphone, the Galaxy S7 as my secure vault. I have a veracrypt container on it containing photos of my credit card, bank card and ID, and also information from those 3 written down. It also holds all my passwords. That's all i use the device for. For further security, i never connect it to the wifi or something else, like Bluetooth.

I'm very soon getting a Galaxy S9 and then i will use the Galaxy S8 as my secure vault and will be selling my Galaxy S7.

At some points, i let down my security and for example, copied the image of my credit card into the preinstalled gallery folder and then deleted it only by using the pre available deleting function. The same with text files that hold for example passwords.

So for my question: i want to delete everything on the device. I want to install a new firmware (Android 8). I already downloaded that.

I took a look at this thread: https://androidforums.com/threads/q...ruth-read-me-first-now-with-ram-truth.906249/ and one app that gets mentioned there states that the Android operation system also uses other storage areas for my radio hardware and other secure functions. So i am wondering where on my device could information be stored? For example: does my smartphone have a graphics card that has own storage build in where it could store information about the images i viewed on my phone or the images themself? The same for text files? Or does my phone simply have only one internal hard drive and one RAM? And i can just plug it into my PC and use a product like secure eraser from ASCOMP to delete the storage my PC shows?

Any information on where i can find answers or direct answers themselves are appreciated

Greetings

 

[El Presidente]

Any information you write to the device is done to the data partition or the SD Card.

If you're selling the device, a simple factory reset is all that's required as 99.99% of people won't be able to recover anything, esepcially if the phone was encrypted before hand (as any device which shipped with Android 6.0 was).

Encrypting and wiping the SD Card will also ensure no data can be recovered.

I say 99.99% because there is specialist equipment available which can read deleted data, but it costs thousands and isn't available to the general public.

 

[El Presidente]

Also, your English is pretty much perfect!

 

[Nath_fiery]

Any information you write to the device is done to the data partition or the SD Card.

If you're selling the device, a simple factory reset is all that's required as 99.99% of people won't be able to recover anything, esepcially if the phone was encrypted before hand (as any device which shipped with Android 6.0 was).

Encrypting and wiping the SD Card will also ensure no data can be recovered.

I say 99.99% because there is specialist equipment available which can read deleted data, but it costs thousands and isn't available to the general public.

Thank you for the help