Chunked Transfers
Normally, when sending back a response the sever has to know everything about the response it is about to send before it sends it. For instance, servers should set the Content-Length header on each response to the length of the response itself. This can be difficult for the server to do if the content is dynamically created (e.g. if it is the output of a CGI script). So in practice servers (including Apache) often do not send a Content-Length with dynamic documents. This has not been a problem with HTTP/1.0, but for persistent connections to work in HTTP/1.1, the Content-Length must be known in advance.
