There are two caches being used for Marble: The physical memory which is needed to keep map data in the computer's memory. Increasing the value will make the application more responsive. The hard disc memory cache is used by download contents from the Internet (e.g. Wikipedia data or map data). Decrease this value if you want to save space on the hard disc and if high usage of the Internet is not an issue.
Proxy settings for your local intranet. Please leave empty if there is no proxy.