Overlapped I/O
Overlapped I/O is a name used for asynchronous I/O in the Windows API. It was introduced as an extension to the API in Windows NT. Utilizing overlapped I/O requires passing an OVERLAPPED structure to API functions that normally block, including ReadFile(), WriteFile(), and Winsock's WSASend() and WSARecv(). The requested operation is initiated by a function call which returns immediately, and is completed by the OS in the background.