Internet Explorer cache settings
Finally, I found a resource that explains Internet Explorer’s cache settings in adequate details. On 14 July 2010, Microsoft Internet Explorer blog published a post titled “Caching improvements in Internet Explorer 9” in which Eric Lawrence described exactly what the caching option in Internet Options of Internet Explorer do. Here is what he says:
Internet Explorer allows the user to configure what should happen when content is delivered without expiration information. Inside Tools > Internet Options > Browsing history > Settings, you will see four options:
These four options have the following behavior:
Every time I visit the webpage Any resource without explicit freshness information is treated as stale and will be revalidated with the server before each reuse. Every time I start Internet Explorer Any resource without explicit freshness information is validated with the server at least once per browser session (and every 12 hours thereafter in that session). Automatically (Default) Internet Explorer will use heuristics to determine freshness. Never Any cached resource will be treated as fresh and will not be revalidated.
Perhaps technical terms like freshness information and (re)validation, which are explain in the original blog post, need to be explained again. Every web server can send metadata along the data that it transmits to your computer. Data can be a web page, an image, a file that you download to your disk for further use, etc. Metadata are usually not shown to you unless you request so but can include the date in which the data is last changed. (To see metadata, use Properties command in Internet Explorer or View Page Info command in Firefox.) One of these metadata is Maximum age of cached contents. When this piece of metadata does not exist, these settings come into play: Internet Explorer has to contact web server to revalidate; that is, to somehow discover whether the cached contents are still the same as those on the server (fresh) or need to be downloaded again (stale). Of course, Internet Explorer may use other pieces of metadata to do this validation, such as Last Modified Date metadata; but contacting web server (per these settings) is still required.
The blog post also promises that Internet Explorer 9 will see an improvement in its caching efficiency in several areas.