L-5.14: Inverted paging | Memory Management | Operating System

Summary

In this video, the concept of inverted paging is explored, comparing it to normal paging in memory management. Normal paging involves multiple page tables for each process, consuming significant memory, whereas inverted paging uses a single global page table for the entire system, reducing memory usage. However, inverted paging introduces slower search times due to the need for linear searching through the global table. The video explains how each system works, their pros and cons, and the reasons behind the limited popularity of inverted paging, despite its memory efficiency.

Takeaways

• 😀 In normal paging, each process has its own page table to map virtual pages to physical memory frames.
• 😀 The page table is stored on the hard disk but must be brought into memory when pages are loaded.
• 😀 The main issue with normal paging is the significant memory consumption due to multiple page tables for each process.
• 😀 In inverted paging, a single global page table is used for all processes, reducing memory usage.
• 😀 The global page table in inverted paging tracks frame numbers, page numbers, and process IDs.
• 😀 In inverted paging, the number of entries in the global page table is equal to the number of frames in physical memory.
• 😀 Each entry in the inverted page table contains the page number and the associated process ID for each memory frame.
• 😀 Searching for a specific page in inverted paging requires linear search through the global page table, which increases search time.
• 😀 Normal paging allows for quick lookups as the page table directly maps page numbers to frames, reducing search time.
• 😀 Inverted paging saves memory by eliminating the need for multiple page tables, but this comes at the cost of slower access times.
• 😀 Despite its efficiency in memory usage, inverted paging is less popular today due to the increasing importance of speed over memory conservation in modern systems.

Q & A

What is the main difference between normal paging and inverted paging?

The main difference is that in normal paging, each process has its own page table that maps virtual pages to physical frames. In contrast, inverted paging uses a global page table, which maps physical frames to the process ID and page number, reducing the need for individual page tables for each process.

What are the key limitations of normal paging?

The key limitations of normal paging include significant memory overhead due to storing a separate page table for each process, and limited available frames in memory because some frames are used for page tables rather than process data.

Why does normal paging require a page table for each process?

In normal paging, each process needs its own page table to map virtual page numbers to physical frame numbers. This allows the CPU to locate pages in the main memory based on the page table associated with the current process.

How does inverted paging optimize memory usage?

Inverted paging reduces memory usage by using a single global page table for all processes, rather than maintaining separate page tables for each one. This eliminates the need to store multiple page tables in memory, saving valuable memory space.

What is a potential downside of using inverted paging?

A potential downside of inverted paging is the increased search time. Since there is only one global page table, finding the correct page requires a linear search through the table, which can slow down performance, especially with large numbers of memory frames.

What information is stored in each entry of the inverted page table?

Each entry in the inverted page table contains the frame number, the page number, and the process ID. This helps identify which page from which process is stored in a given frame.

How does the global page table in inverted paging reduce memory overhead?

By using a single global page table, inverted paging eliminates the need to store individual page tables for each process. This means fewer entries in memory and less space used for managing the mapping of pages to frames, especially in systems with many processes.

Why is search time a problem in inverted paging?

Search time is a problem in inverted paging because finding a specific page requires performing a linear search through the global page table. There is no direct mapping between page numbers and frame numbers, so the system must check each entry to find the correct mapping.

Why is inverted paging not widely used in modern systems?

Inverted paging is not widely used in modern systems because, while it saves memory, it introduces slower search times. Modern systems prioritize performance, and as memory has become cheaper, the efficiency of quick lookups in normal paging outweighs the memory savings of inverted paging.

How does the CPU find the page in normal paging versus inverted paging?

In normal paging, the CPU directly uses the page table to find the physical frame for the requested page. In inverted paging, the CPU must search the global page table to find the correct frame, as the page table is no longer tied to individual processes but to physical frames.