memoryallocation

Memory allocation is the process by which a program obtains memory from the operating system or runtime for data storage during execution. It is typically managed by the operating system, the language runtime, and the program itself. Memory is usually categorized as stack allocation, which is automatic and tied to function scope, and heap allocation, which is dynamic and controlled at runtime.

A program requests blocks of memory from an allocator. The allocator returns a pointer if space is available and may reuse freed blocks. Allocation strategies include first-fit, best-fit, and worst-fit, implemented with free lists, bitmaps, or more advanced structures. Some allocators use a buddy system or region-based approaches to balance speed and space.

Memory management models vary. Manual memory management requires explicit release of resources (for example, malloc and free in C). Automatic memory management relies on a runtime to reclaim unused memory, through garbage collection or reference counting. Many languages mix approaches, using smart pointers or scoped regions.

Fragmentation is a key concern. External fragmentation occurs when free memory is split into small blocks; internal fragmentation happens when allocated blocks are larger than needed. Effective allocators aim to reduce fragmentation and improve locality for cache performance.

Security and reliability concerns include leaks, use-after-free, and double frees. Debugging tools such as sanitizers and memory analyzers help detect these issues.

Understanding memory allocation helps explain performance characteristics of software, especially in long-running processes, real-time applications, and systems with tight resource constraints.