android - What are the differences among Internal storage, external storage, sd card and removable storage?

Question

From the official documentation:

Using the External Storage

Every Android-compatible device supports a shared "external storage" that you can use to save files. This can be a removable storage media (such as an SD card) or an internal (non-removable) storage ...

I'm really confused about this subject. From what I understand, using external storage doesn't necessarily mean to use a removable card, am I right? However, when talking about external storage, it's always referred as "sd card".

I'm developing an app that downloads .mp3 files from the internet. I want to save those files in the phone memory (don't want to use any removable device) but for what I have learned, those files have to be saved in external memory.However, I would like to offer the possibility of importing a file from a removable device. Where and how should I save those files?

Thanks

Answer 1

Difference between Internal Storage, External Storage (aka primary external storage) and Secondary External Storage?

Internal Storage: is storage that is not accessible by the user, except via installed apps (or by rooting their device). Example: data/data/app_packageName

External Storage has two types:

Primary External Storage: In built shared storage which is "accessible by the user by plugging in a USB cable and mounting it as a drive on a host computer". Example: When we say Nexus 5 32 GB.

Secondary External Storage: Removable storage. Example: SD Card.