Windows Web Services is a new feature of Win7, which is yet another web services stack composed of fully flat C API. Mainstream scenario is legacy codes that you want to leverage a web service but unable to layer over a managed bit due to variety of reason you may have. This solution also has a parity with WCF stack so that you have the similar abstractions like Service Model and Channel Stack as such, along with some differences coming from that facts of unmanaged world like Heap, etc.
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Ibrahim