Hi, two remarks on the issues around FPSIM and tcsh: I of course wondered by a line like mov $4..,r0 is accepted by 'as', I naively expected that this should cause an error. I didn't locate the 211bsd 'as' manual, so checked 7th Edition manuals, which can be found under https://wolfram.schneider.org/bsd/7thEdManVol2/ The assembler manual, see https://wolfram.schneider.org/bsd/7thEdManVol2/assembler/assembler.pdf states 6.1 Expression operators The operators are: (blank) when there is no operand between operands, the effect is exactly the same as if a ‘+’ had appeared. So the lexer sees two tokens $4. --> number . --> symbol for location counter and, because the default operator is '+', interprets this as mov $4. + . , r0 which ends up being a number in the 160000 to 177777 range. So 'as' is not to blame, works as designed. Noel Chippa wrote: The answer is: this bug was in 211bsd all the time. Steven Schultz told me that that they simply didn't have a way to test FPSIM because all machines had FPP, and the only way of testing would have been to physically remove the FP11 from a 11/70. With best regards, Walter