Manual:$wgUseFileCache

File Cache: $wgUseFileCache
This will cache static pages for non-logged-in users to reduce database traffic on public sites.
Introduced in version:	Before 1.1.0
Removed in version:	Still in use
Allowed values:	(boolean)
Default value:	false
Other settings: Alphabetical \| By function

Details

Set to true to activate server-side file caching. This will cache static pages for non-logged-in users to reduce database traffic on public sites.

Must set $wgShowIPinHeader = false.

Specify where you want the cache files to go in your server filesystem using $wgFileCacheDirectory . You must create the directory yourself though.