Operating System Questions Medium
Demand paging is a memory management technique used in virtual memory systems to efficiently utilize the available physical memory. It allows the operating system to load only the necessary pages of a process into memory, rather than loading the entire process at once.
In demand paging, the virtual memory is divided into fixed-size units called pages, and the physical memory is divided into fixed-size units called frames. When a process is initially loaded into memory, only a small portion of it, known as the initial pages, are loaded into frames. The remaining pages are stored on secondary storage, such as a hard disk.
When a process requests a page that is not currently in memory, a page fault occurs. The operating system then retrieves the required page from secondary storage and loads it into a free frame in physical memory. This process is known as page swapping.
Demand paging offers several advantages. Firstly, it allows for efficient memory utilization as only the necessary pages are loaded into memory, reducing the amount of physical memory required. This enables the system to run more processes simultaneously, improving overall system performance.
Secondly, demand paging allows for faster process startup times. Since only the initial pages are loaded into memory, the process can start executing sooner, without waiting for the entire process to be loaded.
However, demand paging also has some drawbacks. One major drawback is the occurrence of page faults. When a page fault occurs, the operating system needs to retrieve the required page from secondary storage, which can result in a significant delay in process execution. To mitigate this, various techniques such as page replacement algorithms and pre-fetching strategies are employed to minimize the frequency of page faults.
In conclusion, demand paging is a memory management technique that allows for efficient utilization of physical memory by loading only the necessary pages of a process into memory. It offers advantages such as improved memory utilization and faster process startup times, but also introduces the possibility of page faults, which can impact system performance.