Why do slow downloads via PHP stop after an hour while direct download of the same files do not?

We do not allow users to download files directly (payed files). If the user has a slow connection and the download does take a long time it breaks at about 60-70 minutes (the server closes the connection. If the same download is done directly (directly accessing the file URL instead of sending it via PHP) 开发者_开发知识库the download works just fine. Any ideas?

There's a PHP configuration parameter called max_execution_time that sets the maximum time a PHP script can run before it times out. The default value is 30 seconds, but I suspect yours is set to around 60 minutes.