What is a backing store in the context of module iohttps://docs.python.org/3/library/io.html

[Veek M]

So i was making some notes and: https://i.imgur.com/UATAKXh.png

I did not understand this 

https://docs.python.org/3/library/io.html
'Text I/O expects and produces str objects. This means that whenever the 
backing store is natively made of bytes (such as in the case of a file), 
encoding and decoding of data is made transparently as well as optional 
translation of platform-specific newline characters.'

1. What is a backing store? 
2. How does it fit in/influence what we pass to the fileObject/stream/
filelikeObject.method()

So I've drawn a small dia - but I cannot see a connection between the 
'str' object or 'bytes' object being passed to .write() and the Backing 
Store?

Google just says the backing store is secondary MEMORY - Harddisk cache 
or for paging.. but how does that relate to Python?

I just concluded the backing store was a buffer?