Short for memory management unit, the hardware component that manages virtual memory systems. Typically, the MMU is part of the CPU, though in some designs it is a separate chip. The MMU includes a small amount of memory that holds a table matching virtual addresses to physical addresses. This table is called the Translation Look-aside Buffer (TLB). All requests for data are sent to the MMU, which determines whether the data is in RAM or needs to be fetched from the mass storage device. If the data is not in memory, the MMU issues a page fault interrupt.