OS - Memory Management

Memory management is the functionality of an operating system which handles or manages primary memory. Memory management keeps track of each and every memory location either it is allocated to some process or it is free. It checks how much memory is to be allocated to processes. It decides which process will get memory at what time. It tracks whenever some memory gets freed or unallocated and correspondingly it updates the status.

Memory management provides protection by using two registers, a base register and a limit register. The base register holds the smallest legal physical memory address and the limit register specifies the size of the range. For example, if the base register holds 300000 and the limit register is 1209000, then the program can legally access all addresses from 300000 through 419999.

Instructions and data to memory addresses can be done in following ways

• Compile time -- When it is known at compile time where the process will reside, compile time binding is used to generate the absolute code.
• Load time -- When it is not known at compile time where the process will reside in memory, then the compiler generates re-locatable code.
• Execution time -- If the process can be moved during its execution from one memory segment to another, then binding must be delayed to be done at run time