max number of concurrent file downloads in a browser?

Question

Two related questions:

1. What are the maximum number of concurrent files that a web page is allowed to open (e.g., images, css files, etc)? I assume this va

Answer 1

For Internet Explorer see this MSDN article. Basically, unless the user has edited the registry or run a 'internet speedup' program, they are going to have a maximum of two connections if using IE7 or earlier. IE8 tries to be smart about it and can create up to 6 concurrent connections, depending on the server and the type of internet connection. In JavaScript, on IE8, you can query the property window.maxConnectionsPerServer.

For Firefox, the default is 2 for FF2 and earlier, and 6 for FF3. See Mozilla documentation. I'm not aware of anyway to retrieve this value from JavaScript in FF.

Most HTTP servers have little ability to restrict the number of connections from a single host, other than to ban the IP. In general, this isn't a good idea, as many users are behind a proxy or a NAT router, which would allow for multiple connections to come from the same IP address.

On the client side, you can artificially increase this amount by requesting resources from multiple domains. You can setup www1, www2, etc.. alias which all point to your same web server. Then mix up where the static content is being pulled from. This will incur a small overhead the first time due to extra DNS resolution.