The specific dynamic memory allocation algorithm implemented can impact performance significantly. The memory management system must track outstanding allocations to ensure that they do not overlap and that no memory is ever "lost" (i.e. The allocator's metadata can also inflate the size of (individually) small allocations. Several issues complicate the implementation, such as external fragmentation, which arises when there are many small gaps between allocated memory blocks, which invalidates their use for an allocation request. At any given time, some parts of the heap are in use, while some are "free" (unused) and thus available for future allocations. Memory requests are satisfied by allocating portions from a large pool of memory called the heap or free store.
The task of fulfilling an allocation request consists of locating a block of unused memory of sufficient size. Memory management within an address space is generally categorized as either manual memory management or automatic memory management.
Unix-like operating systems, memory is managed at the application level. OS/360 and successors, memory is managed by the operating system. The quality of the virtual memory manager can have an extensive effect on overall system performance. Virtual memory systems separate the memory addresses used by a process from actual physical addresses, allowing separation of processes and increasing the size of the virtual address space beyond the available amount of RAM using paging or swapping to secondary storage. Several methods have been devised that increase the effectiveness of memory management. This is critical to any advanced computer system where more than a single process might be underway at any time. The essential requirement of memory management is to provide ways to dynamically allocate portions of memory to programs at their request, and free it for reuse when no longer needed. Memory management is a form of resource management applied to computer memory.
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