Simplify the following text for a Grade 9 native English-speaking person.
Original: Since cache pages can be easily dropped and re-used , some operating systems , notably Windows NT , even report the page cache usage as `` free '' memory , while the memory is actually allocated to disk pages . This has led to some confusion about the utilization of page cache in Windows .
Simplified: A page cache or disk cache is a buffer of pages certain operating systems keep in memory .