In connection with memory management OS is responsible for

The part of the operating system which handles this responsibility is called the memory manager. Since every process must have some amount of primary memory in order to execute, the performance of the memory manager is crucial to the performance of the entire system. Virtual memory refers to the technology in which some space in hard disk is used as an extension of main memory so that a user program need not worry if its size extends the size of the main memory.

For paging memory management, each process is associated with a page table. Each entry in the table contains the frame number of the corresponding page in the virtual address space of the process. This same page table is also the central data structure for virtual memory mechanism based on paging, although more facilities are needed. It covers the Control bits, Multi-level page table etc. Segmentation is another popular method for both memory management and virtual memory

Basic Cache Structure : The idea of cache memories is similar to virtual memory in that some active portion of a low-speed memory is stored in duplicate in a higher-speed cache memory. When a memory request is generated, the request is first presented to the cache memory, and if the cache cannot respond, the request is then presented to main memory.

Content-Addressable Memory (CAM) is a special type of computer memory used in certain very high speed searching applications. It is also known as associative memory, associative storage, or associative array, although the last term is more often used for a programming data structure.

In addition to the responsibility of managing processes, the operating system must efficiently manage the primary memory of the computer. The part of the operating system which handles this responsibility is called the memory manager. Since every process must have some amount of primary memory in order to execute, the performance of the memory manager is crucial to the performance of the entire system. Nutt explains: “The memory manager is responsible for allocating primary memory to processes and for assisting the programmer in loading and storing the contents of the primary memory. Managing the sharing of primary memory and minimizing memory access time are the basic goals of the memory manager.”

The real challenge of efficiently managing memory is seen in the case of a system which has multiple processes running at the same time. Since primary memory can be space-multiplexed, the memory manager can allocate a portion of primary memory to each process for its own use. However, the memory manager must keep track of which processes are running in which memory locations, and it must also determine how to allocate and de-allocate available memory when new processes are created and when old processes complete execution. While various different strategies are used to allocate space to processes competing for memory, three of the most popular are Best fit, Worst fit, and First fit. Each of these strategies are described below:

Best fit: The allocator places a process in the smallest block of unallocated memory in which it will fit. For example, suppose a process requests 12KB of memory and the memory manager currently has a list of unallocated blocks of 6KB, 14KB, 19KB, 11KB, and 13KB blocks. The best-fit strategy will allocate 12KB of the 13KB block to the process.

Worst fit: The memory manager places a process in the largest block of unallocated memory available. The idea is that this placement will create the largest hold after the allocations, thus increasing the possibility that, compared to best fit, another process can use the remaining space. Using the same example as above, worst fit will allocate 12KB of the 19KB block to the process, leaving a 7KB block for future use.

First fit: There may be many holes in the memory, so the operating system, to reduce the amount of time it spends analyzing the available spaces, begins at the start of primary memory and allocates memory from the first hole it encounters large enough to satisfy the request. Using the same example as above, first fit will allocate 12KB of the 14KB block to the process.

Notice in the diagram above that the Best fit and First fit strategies both leave a tiny segment of memory unallocated just beyond

 the new process. Since the amount of memory is small, it is not likely that any new processes can be loaded here. This condition of splitting primary memory into segments as the memory is allocated and deallocated is known as fragmentation. The Worst fit strategy attempts to reduce the problem of fragmentation by allocating the largest fragments to new processes. Thus, a larger amount of space will be left as seen in the diagram above.

Another way in which the memory manager enhances the ability of the operating system to support multiple process running simultaneously is by the use of virtual memory. According the Nutt, “virtual memory strategies allow a process to use the CPU when only part of its address space is loaded in the primary memory. In this approach, each process’s address space is partitioned into parts that can be loaded into primary memory when they are needed and written back to secondary memory otherwise.” Another consequence of this approach is that the system can run programs which are actually larger than the primary memory of the system, hence the idea of “virtual memory.” Brookshear explains how this is accomplished:

“Suppose, for example, that a main memory of 64 megabytes is required but only 32 megabytes is actually available. To create the illusion of the larger memory space, the memory manager would divide the required space into units called pages and store the contents of these pages in mass storage. A typical page size is no more than four kilobytes. As different pages are actually required in main memory, the memory manager would exchange them for pages that are no longer required, and thus the other software units could execute as though there were actually 64 megabytes of main memory in the machine.”

In order for this system to work, the memory manager must keep track of all the pages that are currently loaded into the primary memory. This information is stored in a page table maintained by the memory manager. A page fault occurs whenever a process requests a page that is not currently loaded into primary memory. To handle page faults, the memory manager takes the following steps:

Which of the following is are responsibilities of operating system connection with memory management?

Which key component of OS is responsible for managing the memory?

What is memory management system in OS?

What is the role of OS in process management and memory management?