It all comes back to how the kernel can get data back to the caller: https://speakerdeck.com/trent/pyparallel-how-we-removed-the-....
Windows has a distinct advantage thanks to design decisions made in VMS by Cutler et al; namely, I/O via I/O request packets, and much better memory management.
POSIX systems are at a disadvantage because of the readiness-oriented nature of I/O, leaving the caller responsible for "checking back" when something can be done, versus "here, do, this, tell me when it's done". (https://speakerdeck.com/trent/pyparallel-how-we-removed-the-...)
; Preparing to listen the incoming connection (passive socket)
; int listen(int sockfd, int backlog);
; listen(sockfd, 0);
mov eax, 102 ; syscall 102 - socketcall
mov ebx, 4 ; socketcall type (sys_listen 4)
; listen arguments
push 0 ; backlog (connections queue size)
push edx ; socket fd
mov ecx, esp ; ptr to argument array
int 0x80 ; kernel interruption (this is the "receive packet" call along with MOVs above)