Simplify the following text for a Grade 5 native English-speaking person.
Original: The disk buffer is controlled by the microcontroller in the hard disk drive , and the page cache is controlled by the computer to which that disk is attached . The disk buffer is usually quite small , from 2 to 32 MiB , and the page cache is generally all unused physical memory .
Simplified: A disk buffer is a small amount of memory on a hard drive .