They can get away by using fewer servers because those servers do less work. Microsoft's on-line operations are a fraction of the size of Google's.
It's unlikely any OS is significantly better on resource management than any other. OS design books are quite old by now. I remember reading Tannembaum's MINIX while on college, some more than 20 years ago. And, during those 20 something years, desktop computers and x86 servers evolved pretty little. Quite frankly, when compared to what RISC promised in the late 80s and early 90s, it's quite disappointing.
It's unlikely any OS is significantly better on resource management than any other. OS design books are quite old by now. I remember reading Tannembaum's MINIX while on college, some more than 20 years ago. And, during those 20 something years, desktop computers and x86 servers evolved pretty little. Quite frankly, when compared to what RISC promised in the late 80s and early 90s, it's quite disappointing.