Claudio,

IB SuperServer on Windows has 'true' local access, I
believe implemented as shared memory, perhaps carried
over from LIBS.

When SuperServer was implemented on UNIX, IB v5.x (Solaris,
HPUX) the LIBS model was not easily duplicated in UNIX.
Meaning a platform independent way. InterBase attempts
to introduce as little platform dependent code (being
single source) as possible when implementing features.
A decision was made to route 'local access'

(eg connect /dbs/my.gdb)

through tcp loopback

(eg connect localhost:/dbs/my.gdb)

on UNIX SuperServer implementations until a cross platform
(including a re-write of the Windows local access) solution
could be introduced. As it stands the Windows server
still uses the shared memory method instead of routing
a local connection through loopback.

I believe that most of if not all of the above is fact.
I hope that the info helps.

Markus