Memory management

Memory management is the act of managing computer memory. The essential requirement of memory management is to provide ways to dynamically allocate portions of memory to programs at their request, and freeing it for reuse when no longer needed. This is critical to the computer system.
Several methods have been devised that increase the effectiveness of memory management. Virtual memory systems separate the memory addresses used by a process from actual physical addresses, allowing separation of processes and increasing the effectively available amount of RAM using paging or swapping to secondary storage. The quality of the virtual memory manager can have a big impact on overall system performance.


The task of fulfilling an allocation request consists of finding a block of unused memory of sufficient size. Even though this task seems simple, several issues make the implementation complex. One of such problems is internal and external fragmentation, which arises when there are many small gaps between allocated memory blocks, which are insufficient to fulfill the request. Another is that allocator's metadata can inflate the size of (individually) small allocations; this effect can be reduced by chunking.
Usually, memory is allocated from a large pool of unused memory area called the heap (also called the free store). Since the precise location of the allocation is not known in advance, the memory is accessed indirectly, usually via a pointer reference. The precise algorithm used to organize the memory area and allocate and deallocate chunks is hidden behind an abstract interface and may use any of the methods described below.


The dynamic memory allocation algorithm actually used can impact performance significantly and a study conducted in 1994 by Digital Equipment Corporation illustrates the overheads involved for a variety of allocators. The lowest average instruction path length required to allocate a single memory slot was 52 (as measured with an instruction level profiler on a variety of software).