Memory management in operating systems

Historically, main memory has always been significantly more expensive than secondary storage, and system designers have tried to optimise its use. Although costs have fallen steadily, this is still the case today, and modern operating systems and applications require large amounts of memory in order to run.

Memory management in operating systems

You can help by adding to it. November Application-level memory management is generally categorized as either automatic memory management, usually involving garbage collectionor manual memory management.

Dynamic memory allocation[ edit ] See also: C dynamic memory allocation The task of fulfilling an allocation request consists of locating a block of unused memory of sufficient size.

Memory requests are satisfied by allocating portions from a large pool of memory called the heap or free store. Several issues complicate the implementation, such as external fragmentationwhich arises when there are many small gaps between allocated memory blocks, which invalidates their use for an allocation request.

This is often managed by chunking. The memory management system must track outstanding allocations to ensure that they do not overlap and that no memory is ever "lost" i. Efficiency[ edit ] The specific dynamic memory allocation algorithm implemented can impact performance significantly.

A study conducted in 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.

The specific algorithm used to organize the memory area and allocate and deallocate chunks is interlinked with the kerneland may use any of the following methods: Fixed-size blocks allocation[ edit ] Main article: Memory pool Fixed-size blocks allocation, also called memory pool allocation, uses a free list of fixed-size blocks of memory often all of the same size.

This works well for simple embedded systems where no large objects need to be allocated, but suffers from fragmentationespecially with long memory addresses. Buddy memory allocation In this system, memory is allocated into several pools of memory instead of just one, where each pool represents blocks of memory of a certain power of two in size, or blocks of some other convenient size progression.

All blocks of a particular size are kept in a sorted linked list or tree and all new blocks that are formed during allocation are added to their respective memory pools for later use.

If a smaller size is requested than is available, the smallest available size is selected and split.

Memory management in operating systems

One of the resulting parts is selected, and the process repeats until the request is complete. When a block is allocated, the allocator will start with the smallest sufficiently large block to avoid needlessly breaking blocks.

When a block is freed, it is compared to its buddy. If they are both free, they are combined and placed in the correspondingly larger-sized buddy-block list.In early multi-programming systems, the memory management function had to protect the operating system memory space from all user processes loaded into memory as before, but it now also had to protect those user processes from each other.

In operating systems, memory management is the function responsible for managing the computer's primary memory.

Overview — Memory Management Reference documentation

[1]: pp– The memory management function keeps track of the status of each memory location, either allocated or free. In this chapter is a quality overview of memory management and operating systems you can use to improve your grades, excel on a test or complete an assignment.

Memory Management & Operating Systems Chapter Exam Instructions. Choose your answers to the questions and click 'Next' to see the next set of questions. + Operating system needed to check if routine is in processes’ memory address.

+ Dynamic linking is particularly useful for libraries. Memory Management Performs the above operations. ECE Operating Systems 5 Logical vs. Physical Address Space •A logical address space that is bound to a separate physical address space – Logical address – generated by the CPU; also referred to as virtual address.

– Physical address – address generated by the memory management unit. • Logical and physical addresses are the same.

Memory management - Wikipedia