IO completion ports (IOCP) was such a brilliant design, and still holds up today. It's fascinating how long it took for similar paradigms to become more dominant elsewhere eg with kqueue
See another recent thread for my theory (based on what I heard from various Unix vendors at the time) that this was mostly due to fear of MS patent litigation. iirc AIX did have an IOCP-like feature. MS acquired the rights to DEC's patents in this space, handy since IOCP is similar to VMS's QIO.
