From: fuer@nessie.gud.siemens.co.at (Gerhard Fuernkranz) Subject: Re: Coherent vs. Linux - a comparo Date: Mon, 28 Jun 1993 11:30:59 GMT
H.P. Heidinger (hph@hphbbs.E.open.DE) wrote:
: Show me a "nowadays-UNIX" that clings to ONE standard!
:
: - IRIX (Silicon-Graphics) is a so-far "pure Sys-V" but has
: symbolic-links in its filesystem,
:
: - ULTRIX is a BSD[V4.2]-derivate but has a 'termio.h' and
: 'termios.h' (POSIX-termio) and supports all these
:
: - TOS [Targon-Operating-System, Unix-clone] V4.whatsoever on NIXDORFs
: TARGON (actually a PYRAMID-machine) even has a file /etc/universe
: that keeps entries about which 'universe' certain users prefer to
: work in -- "att" (AT&T) or "bsd". You find an /etc/inittab and
: /usr/ucb/... on the VERY SAME machine!
"UNIX" itself is _not_ a standard. But there exist standards like
POSIX or XOPEN and many "nowadays-UNIXes" are POSIX and/or XOPEN compliant.
E.g. SVR4 is both POSIX and XOPEN compliant and so should be all its
derivatives.
Things like /etc/inittab, etc. are _not_ specified in the standards and
are therefore implementation dependent (and may be different on different
platforms).
When an application uses nothing but system calls / library functions
defined in the API of these standards, then it will be easy to port
this application to all the platforms, that comply to the standards.
Unfortunately some programs - especially system software - need more
functions than than the standards define, so these programs cannot
be written "portable" (conforming to a standard).