Newsgroups function by a large network of servers which regularly synchronize posts with each other. Each time a post is transferred between news servers there is a chance that it will be dropped. There are many possible causes for a dropped post, such as high network traffic and dropped packets. If even a single post is dropped from a large file then the entire file will become useless. To combat this, par files were created.
Many ISP News Servers do not have a link into the Internet backbone of the internal news network. They often suffer from resulting low completion rates.
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