The world is dotted with news servers. From time to time (hourly or
sometimes less) they compare notes with their neighbours and update
themselves with whatever is new. That way a new article will spread
around the world very rapidly. Subscribers are posting new articles to
various servers all the time and copies of these are being
interchanged and passed along in an almost continuous process.
In the context of Usenet, Google is just one more server. Some
articles start with Google and hopefully copies spread from there.
Other articles start a long way from Google but, equally hopefully,
copies should end up with Google in short order.
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Regards,
Eric Stevens