On Apr 29, 2020, at 12:08 AM, Jacob Ritorto &lt;jacob.ritorto(a)gmail.com&gt; wrote: Shoot, celebrated too soon. I rearranged it per your tutelage, Ron, and it's still giving an Illegal Instruction error! From the adb output it looks like it's balking at the "14" instruction at location 24, which, based on the BSD updates you mentioned, I thought should've been taken as an arg, not an instruction, right? I assume this worked for you on some BSD, right? If so, is it a bug in the recent 2.11BSD patch release, perhaps? Anyone able to help me understand? "hello.s" 8 lines, 52 characters sys 4 1 a 6 sys 1 0 a: <Hello\n> "hello.s" 7 lines, 78 characters as hello.s Illegal instruction (core dumped) 0000000 000407 000022 000000 000000 000010 000000 000000 000000 0000020 104404 000001 000014 000006 104401 000000 062510 066154 0000040 005157 000000 000000 000002 000000 000000 000000 000000 0000060 000000 000000 000000 000004 000002 000014 000000 000006 0000100 000141 0000102 adb> :s stopped at 0: sys write adb> :s a.out: running stopped at 04: <illegal op> 014 adb> :s a.out: running Illegal instruction stopped at 06: rtt adb> :s a.out: running Illegal instruction - core dumped process terminated adb> > On Tue, Apr 28, 2020 at 10:26 PM Noel Chiappa &lt;jnc(a)mercury.lcs.mit.edu <mailto:jnc@mercury.lcs.mit.edu>> wrote: Sounds like a perfect topic for a CHWiki page. :-) E.g. this one: http://gunkies.org/wiki/Unix_V6_internals <http://gunkies.org/wiki/Unix_V6_internals> which I did as a bit of an addendum to Lions, to explain rsav, qsav and ssav, and similar topics. I noticed in the comparison of your two binary files that the instructions looked the same, but the a.out headers had a difference, but I didn't remember the fields in the a.out header enough to know what the differences meant. I thought I remembered doing an a.out page there, but apparently not. I thought about doing one now, but decided it wasn't worth it; I just needed to spin up my V6 system and do 'man a.out'! :-) Noel