>They developed hardware optimized to run FORTRAN, including machine instructions that directly implemented FORTRAN's distinctive 3-way branch operation [=Arithmetic IF]

Hahaha oh wow. That's amazing. Fun fact:

Arithmetic IF makes handling exit codes significantly less annoying¹, and that's because Arithmetic IF is how we came to get signed integers as exit codes in the first place.

¹at least in theory, in practice half the people implement the codes incorrectly because they don't realize this, and so…

Apple II as well. When displaying text, bit 7 determined if the text was flashing (0) or normal (1). (There was also inverse with bit 7 and bit 6 clear). Since bit 7 had to be set to display normally, some text editors saved their ASCII text files with bit 7 set.

It’s funny how you describe it as “ASCII with the top bit set”. As in, by default ASCII doesn’t have the top bit set. You can have malformed Unicode too. There are plenty of invalid ranges defined in the UTF-8 spec, does that mean that UTF-8 is just a convention and those malformed pieces are counterexamples to the convention?

Holy cow. Never in my wildest dreams did I ever think I'd ever hear of PRIMOS again.