MEMORY MANAGEMENT UNIT (MMU)

The function of a memory management unit is to convert logical memory address into actual physical (real) memory address and provide protection.The MMU is a hardware component placed in between the processor and the main memory.some modern CPUs contain on-chip MMU such as 80286,80386,68030 etc. The CPU which does not contain on-chip MMU uses external MMU. The MMU is used in a mutliprogramming or multiuser system.The tasks which are performed by MMU can be performed by the operating system.Then the operating system.Then the operating system will not get sufficient time for program execution and its other tasks. The MMU reduces the burden of the operating system.the memory addresses used in a program are logical addresses.They indicate the logical position of instructions and data in the program. A logical address is the logical position of instructions and data in the program.A logical address is the location of an instruction or data relative to the program.A logical address is the location of an instruction or data relative to the beginning of the program.

when a  program is compiled each logical address is represented by a memory pointer consisting of two components.In a segment oriented system the two components are:segment selector and offset.In a page oriented system the two components are:page address and page offset.In a page oriented system the two components are:page address and page offset.In other words a logical address is represented by a page number and a page offset.