I have made a prototype for overlapped IO that works with a modified version of Takano Akio's SSC library. I have been trying to add it to GHC's IO implementation but there are some issues. Instead of file descriptors windows handles are needed. The GHC handle implementation is currently based around fd's and many functions would need a separate windows API version. In some cases there is no simple conversion of existing functionality like the binary/text modes. An additional complication is that Haskell handles can be a lot of things other than files. Finally, a threaded rts is needed for the worker pool that processes the IO completions, so the current single threaded IO support must also remain. So for now i am focusing on testing and improving the prototype with a separate IO library. Best regards, Felix