It used the Pascal calling convention, however Lisa and Mac OS were implemented in a mix of Pascal and Assembly.
Pascal UCSD also used a mix of interpreter and later AOT compiler.
Most mainframes don't use C as their original implementation language, and the oldest still being sold (Unisys ClearPath MCP) was designed about 10 years before C was born, in an Algol derived language, that uses instrics instead of Assembly.
If one broadens their horizons beyond UNIX, and looks into the history of computing there are plenty of interesting languages and OS architectures to dive into.
The Internet is full of digitalized version of papers and computer manuals from those days.
Pascal UCSD also used a mix of interpreter and later AOT compiler.
Most mainframes don't use C as their original implementation language, and the oldest still being sold (Unisys ClearPath MCP) was designed about 10 years before C was born, in an Algol derived language, that uses instrics instead of Assembly.
If one broadens their horizons beyond UNIX, and looks into the history of computing there are plenty of interesting languages and OS architectures to dive into.
The Internet is full of digitalized version of papers and computer manuals from those days.