Memory Allocation Methods

Memory allocation methods determine how operating systems assign memory to processes and manage free memory space. The main memory allocation techniques include contiguous allocation (each process occupies a single contiguous block of memory), paging (memory divided into fixed-sized pages, processes divided into same-sized frames), segmentation (memory divided into variable-sized segments matching program structure), and combined systems (paged segmentation or segmented paging). Contiguous allocation can use fixed partitioning (memory divided into fixed-sized partitions) or variable partitioning (memory divided into variable-sized partitions as needed). Variable partitioning uses placement algorithms like first-fit (allocate the first hole that's big enough), best-fit (allocate the smallest hole that's big enough), worst-fit (allocate the largest available hole), and next-fit (similar to first-fit but starts searching from last allocation position). Non-contiguous allocation methods like paging and segmentation avoid external fragmentation but require hardware support for address translation. Modern systems typically use paging with virtual memory, often combined with segmentation for protection and sharing. Memory allocation also involves managing free memory through data structures like bitmaps (each bit represents whether a memory unit is free or allocated) or linked lists (maintain list of free memory blocks). The choice of allocation method affects memory utilization, fragmentation, system performance, and implementation complexity.