"//" in pathnames---standard? & why?

[Guy Harris]

>Is it standard to use two slashes "//" instead of one slash "/" in
>absolute pathnames to represent the root directory?

No!  In fact, POSIX specifically says that "A 'pathname' that begins
with two successive 'slashes' may be interpreted in an
implementation-dependent manner."  There exists systems (Apollo's
systems begin among them, and I think there exist others) that treat
"//machine_name/dir/dir/.../file" as referring to a file in the
directory "/dir/dir/.../file" on machine "machine_name"s file systems.