1. Is mesg or an equivalent available in v7?
its not part of the C stdio library and by te
2. If not, what was the v7 way of putting strings out?
_puts declared as an external
3. Why aren't the system call names defined?
Ah .. you want the DEC assembler ;-) By the time of V5/V6 assembler is starting to have less importance and by V7, little if anything is left.
4. What was the v7 way of naming system calls?
_XXX where XXX is the system call declared as a global.