[TUHS] as(1) on Ultrix-11 vs 2.11BSD

Hiya! Got these two pdp11s, one an 11/23 (Ultrix-11 3.1) and the other an 11/84 (2.11BSD) On the Ultrix machine, I can enter an assembly language program, assemble it and run it fine. amnesiac# cat hello.s mov $1,r0 sys 4 a 6 sys 1 a: <Hello\namnesiac# od hello 0000000 000407 000022 000000 000000 000014 000000 000000 000000 0000020 012700 000001 104404 000014 000006 104401 062510 066154 0000040 005157 000000 000000 000000 000002 000000 000000 000000 0000060 000000 000000 000141 000000 000000 000000 000002 000014 0000100 amnesiac# ./hello Hello amnesiac# But on the BSD machine, the exact same source program assembles differently and crashes with Illegal instruction when I run it. mov $1,r0 sys 4 a 6 sys 1 a: <Hello\n0000000 000407 000022 000000 000000 000010 000000 000000 000000 0000020 012700 000001 104404 000014 000006 104401 062510 066154 0000040 005157 000000 000000 000000 000002 000000 000000 000000 0000060 000000 000000 000000 000004 000002 000014 000000 000006 0000100 000141 0000102 Illegal instruction (core dumped) Anyone know what I'm doing wrong? thx jake