instability in Berkeley versus AT&T releases

[Guy Harris]

> Surprise, Guy, but 4.2BSD really CAN run many V6 binaries. ...However, this
> is misleading.

Certainly is.  4.2BSD can run PDP-11 V6 binaries (there are other V6
binaries), but V7 can't.  ("stat" changed radically, and unlike the
V7/4.2BSD change to "stat" it isn't source-compatible or binary-compatible.
"seek" got replaced by "lseek".)  4.2 can do it because the
compatibility-mode emulator simulates the system calls, and can simulate V6
calls as well as V7 ones.

> not on a Sun or other 4.2BSD machine (where you won't find zork or chess.)

For what it's worth, my Sun UNIX 2.0 manual has a section CHESS(6) -
somebody here rewrote the assembler-language part of "chess" in 68000
assembler language.

> Nonetheless, most V7 programs will compile and run happily on 4BSD, which
> is not true of System V.

Depends on how you define "most".  V7 programs which assume "read"s and
"write"s on slow devices return EINTR when a signal breaks through them
don't run happily on 4.2BSD.  S5 programs that don't use any library
routines not in V7 (other than "strchr"/"strrchr") and don't do terminal
"ioctl"s will (modulo a couple of exceptions, I suspect) compile and run
happily on V7, 4.1BSD, 4.2BSD, ... (S5 programs that *do* use library
routines not in V7 won't work, but then 4.2BSD programs which use library
routines not in V7 won't work on V7 or S5 either.)

	Guy Harris