Back in the days I did a lot of assembly programming for the CDC 6400/6600 computers. The instruction set was simple, but processor flow wasnt. IIRC there wer

Back in the days I did a lot of assembly programming for the CDC 6400/6600 computers. The instruction set was simple, but processor flow wasnt. IIRC there were 3 or so integer units and 1 floating point unit. If a result wasnt ready when an instruction needed it, the processing flow would stall until it was ready. So you needed to remember the instruction timings for each of the models, how many processing unit you were using, etc. to get maximum thruput. This is stuff that a compiler does easily, humans less so. Part of my team was writing hand tuned libraries and part was writing the compilers to produce optimal code. I got to see the trade-offs. Rick James, now at Yahoo, was the king of assembly. He wrote a character move library that was faster than the character move hardware, $100K add-on. He kept getting poached from my projects, because, even at CDC, there weren't many as good as he was. Then there is the productivity issue. The HLC programmer can produce 10x the number of instructions more than the assembly programmer.