Where does the second slash // come from?

Question

linux

Today I accidentally entered two slashes and got an unusual result

[email protected] / # 
cd //
[email protected] // # 
три слеша дает более обычный результат
 cd ///
[email protected] / #
Вопрос 
1. почему два слеша система считает нормальной
2. Где сделал  редирект с большего количества слешей на 1 ?

Answer 1

POSIX.2, in its description of 'cd', says that three or more leading slashes may be replaced with a single slash when canonicalizing the current working directory.
This is, I presume, for historical compatibility. Certain versions of Unix, and early network file systems, used paths of the form //hostname/path to access 'path' on server 'hostname'.
A pathname that begins with two successive slashes may be interpreted in an implementation-defined manner, although more than two leading slashes shall be treated as a single slash.
stackoverflow.com/questions/20690828/what-does-dou...