How programmers in past had created operating systems and advanced software ?

Question

Nowadays programming languages are more complicated than in past, they consume long time to learn, with many advanced topics.

So how programmers did software and operating systems with programming languages using the old programming languages with old features ?

Answer 1

I wouldnt say they are more complex, but rather more abstract. For example, if i wanted to write this in asm:

int square(int value)
{
return value * value;
}

It would look like this:

push ebp
mov ebp, esp
sub esp, 16
mov eax, dword ptr ss:[ebp+8]
imul eax, eax
mov esp, ebp
pop ebp
ret

Which may seem more complicated to some people.

Answer 2

Long but with logical flow and can be understood.
However for some new language features (such as lambda, delegates in c#) I find little hard to understand them and their usages