Cache memory.

A special high speed memory area, that stores the most recently used data and instructions.

The advantage with cache is it speeds up the processing of data.  The disadvantage is it adds to the cost of the computer.

Flash RAM.

Flash RAM is a special type of memory that is not volatile, but it can be changed.

It is often used for special applications such as in digital cell phones.

Virtual memory.

Virtual memory breaks a program into parts and stores some on a secondary storage device and brings it back into memory when needed.

It helps to expand the ability of a computer to handle larger programs