instability in Berkeley versus AT&T releases

[Mark Horton]

In article <2503 at sun.uucp> guy at sun.uucp (Guy Harris) writes:
>> Judging by how much stuff Bell broke when they came out with SV, and
>> judging by the fact that BSD is still sufficiently compatible that you
>> can run a V6 binary on it (2BSD, but 2 is source compatible with 4),
>
>"V6 binary"?  What have you been smoking?  For one thing, 2BSD is V7, not V6
>(I think 1BSD was the V6 Berkeley distribution), but, more importantly, you
>*can't* run V6 binaries on V7.  You don't even have a good chance of
>compiling *source* written for V6 on a V7 system and having it run.

Surprise, Guy, but 4.2BSD really CAN run many V6 binaries.  For example,
look at /usr/games/lib/dungeon and /usr/games/lib/chess, which are invoked
by /usr/games/zork and /usr/games/chess, respectively.  I've also copied
some other V6 style binaries over and run them successfully.

However, this is misleading.  In the first place, dungeon is really an RSX-11
binary (from a Fortran source) which was munged into a V6 binary which was
in turn munged into a V7 binary (the differences between V6 and V7 binaries
really aren't that great), and chess is really a V7 binary.

In the second place, what's really happening here is that these binaries are
PDP-11 binaries (that's what V6 and V7 ran on) which are run in VAX
compatibility mode (the VAX hardware supports such a thing) using a program
called /usr/games/lib/compat and a front end to open the files.  The
hardware does not support split I/D, and of course this only works on a VAX,
not on a Sun or other 4.2BSD machine (where you won't find zork or chess.)

In the third place, there are several incompatibilities between 4.2BSD and
earlier releases of UNIX, such as 4.1BSD, 3BSD, V7, and V6.  Most of these
compatibilities are at the source level, so if you can get past the compiler,
a lot of things are simpler.  Nonetheless, most V7 programs will compile and
run happily on 4BSD, which is not true of System V.