> What's the difference between file descriptors and handles? Both are just opaque numeric identifiers.

The main difference I know of is that file descriptors are sequential, while handles are random. That is, a function like open() will always return the lowest-numbered available file descriptor, while CreateFile() can return any available handle.

Other than that, both are basically identical as far as I know: both are just keys to an in-kernel table which points to the real object.