Mäluhaldusskeemid

Mäluhaldusskeemid, or memory management schemes, are techniques used by computer operating systems to control and allocate main memory (RAM) to various running processes and the operating system itself. The primary goal is to efficiently utilize available memory, prevent processes from interfering with each other's memory spaces, and ensure that programs have access to the memory they require.

One fundamental concept is physical address mapping, where each byte of memory has a unique address. However, many memory management schemes introduce logical addresses, which are what a program "sees" and uses. The memory management unit (MMU) within the CPU translates these logical addresses into physical addresses.

Common memory management schemes include contiguous allocation and non-contiguous allocation. In contiguous allocation, each process is allocated a single, continuous block of memory. While simple, this can lead to external fragmentation, where free memory is broken into small, unusable chunks. Paging is a popular non-contiguous allocation technique. It divides both logical and physical memory into fixed-size blocks called pages and frames, respectively. A process's pages can be scattered throughout physical memory, eliminating external fragmentation. Segmentation is another scheme that divides memory into logical units called segments, often corresponding to program modules or data structures.

Virtual memory is a more advanced concept that extends the apparent size of main memory by using secondary storage (like a hard disk) as an extension of RAM. This allows the system to run programs larger than physical memory and improves multiprogramming by keeping only active parts of programs in RAM. Paging and segmentation are often used in conjunction to implement virtual memory. The choice of memory management scheme significantly impacts system performance, complexity, and security.