The most recently viewed Pages are kept in the memory-resident Page Cache. A page lives in the cache from the moment navigation to its URL is initiated until it is dismissed, replaced or is aged out of cache. The least-recently-used page is aged out of cached when a new page load causes the number of pages in cache to exceed the maximum cache size.
The Page Cache size is set by the PagesToCache property. The minimal setting is 1, since the cache holds at least the current visible page.
The maximum page cache size is controlled by the PagesToCache property.