configuring e-tags

Question

I am using Yslow as a simple speed benchmarking tool and I came across a really confusing concept. The E-tag

So the main problem is : How do I configure E-tags? my grade

Answer 1

Think of E-Tags as a sort of hash. When a browser makes a request for a resource, it sends along the E-tag of the file version it has cached. If the server decides that the files are similar enough (there are "strong" and "weak" versions of E-Tags so it's not always a simple comparison check) it will send a "304 Not Modified" response to the client, rather than the resource itself. This translates into a speed boost, since it prevents bandwidth from being wasted on unchanged files.

E-Tags are sent via HTTP headers.

There's a good example of E-Tags at work (and also how to disable them for Apache) here: http://www.askapache.com/htaccess/apache-speed-etags.html