Introductiom To Paging
PAGING
Paging is a function of memory management where a computer will store and retrieve data from a device’s secondary storage to the primary storage. Memory management is a crucial aspect of any computing device, and paging specifically is important to the implementation of virtual memory.
There are two different types of computer memory; primary and secondary. Primary storage data is temporary and is frequently accessed by applications or other hardware systems. It is typically stored in random access memory (RAM) for fast retrieval. Secondary storage is where data in a computer is kept for longer periods of time. Secondary storage is typically slower than primary. A typical example of secondary memory could be a solid-state drive (SDD), for example.
Virtual memory, what paging is used for often, is a memory management technique where secondary memory can be used as if it were a part of the main memory. Paging acts as an important part of virtual memory, as it allows programs in secondary storage to exceed the available size of the physical storage.
Paging with Example
In Operating Systems, Paging is a storage mechanism used to retrieve processes from the secondary storage into the main memory in the form of pages.
The main idea behind the paging is to divide each process in the form of pages. The main memory will also be divided in the form of frames.
One page of the process is to be stored in one of the frames of the memory. The pages can be stored at the different locations of the memory but the priority is always to find the contiguous frames or holes.
Pages of the process are brought into the main memory only when they are required otherwise they reside in the secondary storage.
Example
Let us consider the main memory size 16 Kb and Frame size is 1 KB therefore the main memory will be divided into the collection of 16 frames of 1 KB each.
There are 4 processes in the system that is P1, P2, P3 and P4 of 4 KB each. Each process is divided into pages of 1 KB each so that one page can be stored in one frame.
Initially, all the frames are empty therefore pages of the processes will get stored in the contiguous way.
Frames, pages and the mapping between the two is shown in the image below.
Let us consider that, P2 and P4 are moved to waiting state after some time. Now, 8 frames become empty and therefore other pages can be loaded in that empty place. The process P5 of size 8 KB (8 pages) is waiting inside the ready queue.
Given the fact that, we have 8 non contiguous frames available in the memory and paging provides the flexibility of storing the process at the different places. Therefore, we can load the pages of process P5 in the place of P2 and P4.
How paging works
Paging works by writing data to, and reading it from, secondary storage for use in primary storage. Paging is a basic function in memory management for a computer's operating system (OS) as well -- this includes Windows, Unix, Linux and macOSs.
In a memory management system that takes advantage of paging, the OS reads data from secondary storage in blocks called pages, all of which have identical size. The physical region of memory containing a single page is called a frame. When paging is used, a frame does not have to comprise a single physically contiguous region in secondary storage. This approach offers an advantage over earlier memory management methods, because it facilitates more efficient and faster use of storage.
