The basic idea behind I/O completion ports as far as I understand it is the following:

In a classic server setup, you''ve got loads of ports, and to check which one has data waiting you call select() or poll() with an fdset of sockets you want to wait on.
The problem with this approach is that it doesn''t scale really well because you have to walk the array of sockets again and again.

With I/O completion ports, however, you''ve got only a single socket or pipe or whatever to wait on. Everytime a packet arrives for your application, the kernel writes a small data structure with the socket # and additional information to that pipe.

The WinNT implementation of IOCP has some additional features like automatic thread pool management, and it can be used for more than sockets (e.g. you can use it for file access as well). I don''t know the implementation details for WinNT, so my description might be a little off, but it''s the basic idea that counts

Unfortunately, IOCP is neither supported on Win9x nor on Linux (though work is in progress).

cu,
Prefect

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