What is Memory Management in OS ?

Editor — Tue, 20 Jul 2021 08:55:58 +0000

Memory management is the process of controlling and coordinating computer memory, assigning portions called blocks to various running programs to optimize overall system performance.
Memory management resides in hardware, in the OS (operating system), and in applications.
In hardware, memory management involves components that physically store data, such as RAM chips, memory caches,etc.,.
In the OS, memory management involves the allocation (and constant reallocation) of specific memory blocks to individual programs as user demands change.
At the application level, memory management ensures the availability of adequate memory for the objects and data structures of each running program at all times.Application memory management combines two related tasks, known as allocation and recycling.
- Allocation : When the program requests a block of memory, a part of the memory manager called the allocator assigns that block to the program.
- Recycling : When a program no longer needs the data in previously allocated memory blocks, those blocks become available for reassignment. This task can be done manually (by the programmer) or automatically (by the memory manager).

Fragmentation

As processes are loaded and removed from memory, the free memory space has broken into small pieces.
That processes cannot be allocated to memory blocks considering their small size and memory blocks remains unused.
This problem is known as Fragmentation.There are two types of fragmentation,
- Internal fragmentation
- External fragmentation

Internal and External fragmentation in os

Memory block assigned to process is lager. Memory is left unused in some portion as it cannot be used by another process.

Total memory space is enough to satisfy a request or to reside a process in it, but it is not contiguous, so it cannot be used.

Editor — Tue, 20 Jul 2021 08:48:34 +0000

Caching is an area of a computer’s memory devoted to temporarily storing recently used data.
In caching the content are which includes HTML pages, images, files and Web objects, is stored on the local hard drive in order to make it faster for the user to access it, which helps to develop the efficiency of the computer and its overall performance.
For example, when a user returns to a Web page they have recently accessed, the browser can pull those files from the cache instead of the original server because it has stored the user’s activity.
The storing of that information saves the user can getting to it faster, and less time to the traffic on the network.

When a cache client wants to access data, it first checks the cache. Cache hit is known as when the requested data is found.
The current of attempts that result in cache hits is known as the cache hit rate or ratio.
If the requested data isn’t found in the cache a situation known as a cache miss. It is getting from main memory and through into the cache. How this is done, and what data is ejected from the cache to make room for the new data, depends on the caching algorithm or policies the system uses.

Caching Memory

Web browsers, such as Internet Explorer, Firefox, Safari and Chrome, use a browser cache to develop performance of frequently accessed webpages.
When we visit a webpage, the requested files are stored in computing storage in the browser’s cache.
Clicking back and returning to a previous page enables from the browser to retrieve most of the files it needs from the cache instead of having them all resent from the web server.
This approach is called read cache. The browser can read data from the browser cache much faster than from the webpage it can reread the files.

Some examples of cache algorithms they are,
- Least Frequently Used (LFU)
- Least Recently Used (LRU)
- Most Recently Used (MRU)

Keeps track of how often an entry is accessed. The data that has to use lowest count gets then removed first.

Puts recently accessed data to near the top of the cache. When the cache reaches its limit, the least recently accessed data are removed.

Removes the most recently accessed data first. This approach is best when older items are more likely to be used.