What is gzip compression?
I did a bit of research today and have some links for you concerning gzip-compression and why you should be using it on your server. First of all, DevArticles has some good resources on compressing web output for Apache 1.3.x (using mod_gzip) and Apache 2.0.x (using mod_deflate).
In a WebRef article, HTTP Compression Speeds up the Web, I found that any browser that supports HTTP 1.1 also supports web compression.
Is Compression Built into the Browser?
Yes. Most newer browsers since 1998/1999 have been equipped to support the HTTP 1.1 standard known as "content-encoding." (although content encoding was included in the HTTP 1.0 spec: RFC 1945). Essentially the browser indicates to the server that it can accept "content encoding" and if the server is capable it will then compress the data and transmit it. The browser decompresses it and then renders the page.
Good stuff to know.