L-5.17: Segmentation Vs Paging | Segmentation Working | Operating system

Summary

The video explains the concept of segmentation in memory management, comparing it to paging. Segmentation divides a process into logical parts based on functionality, unlike paging which divides processes into fixed-size pages. Segmentation allows related data to stay together, offering better efficiency from the user's perspective. The video also discusses how CPU-generated logical addresses are converted into physical addresses through a segment table. It highlights the key differences between paging and segmentation, particularly in terms of flexibility and how data is organized in memory.

Takeaways

• 🧠 Segmentation is a method used to divide a process into parts, which are then loaded into the main memory.
• 📋 Segmentation differs from paging in that it organizes code based on logical units (e.g., functions), while paging divides processes into fixed-sized pages without regard to content.
• 📏 Pages in paging are always the same size, while segments in segmentation can vary in size depending on the code structure.
• 🔄 In paging, a function or module might be split across different frames, which can cause issues when a complete function isn't loaded into the CPU.
• ⚡ Segmentation is more efficient in preserving the integrity of functions or code blocks since it keeps related code within the same segment.
• 📚 CPU generates a logical address that the memory management unit (MMU) uses to convert into a physical address through a segment table.
• 🔢 The segment table contains the base address and size of each segment, helping in locating the segment in the main memory.
• ⚠️ The CPU checks if the requested size (d value) is within the segment's limit. If the d value exceeds the segment size, an error or trap occurs.
• 🧩 Segments are placed non-contiguously in memory, meaning they can be stored at different locations.
• 💡 The primary advantage of segmentation is that it considers the user's perspective, organizing code logically rather than based solely on size, unlike paging.

Q & A

What is segmentation in the context of memory management?

Segmentation is a method in which a process is divided into segments, which are then loaded into the main memory. Each segment represents a logical unit like a function or module, and the segments can vary in size depending on the code.

How does paging differ from segmentation?

Paging divides a process into fixed-size pages without considering the logical structure of the code. In contrast, segmentation divides a process into variable-sized segments based on the user's logical view, such as functions or modules, allowing related data to stay together.

What problem can occur when using paging for a process?

With paging, parts of a function or module may be placed in different memory locations. For example, if the CPU executes one page of a function but not the entire function, it may need to fetch the next page quickly. This can lead to issues like page faults if the next page is not readily available, interrupting the execution flow.

Why is segmentation considered more efficient than paging in some cases?

Segmentation works from the user's point of view, ensuring that related code, such as functions, stays together in one segment. This avoids the fragmentation that can occur in paging, where related code is split across multiple pages, and minimizes page faults.

What is the role of the CPU in segmentation?

The CPU generates a logical address that needs to be converted into a physical address. This conversion is done using a segment table, which helps locate the segment in the main memory based on the logical address provided by the CPU.

What are the two components stored in a segment table?

A segment table contains two components: the base address, which indicates where a segment starts in the main memory, and the size (or limit), which indicates the segment’s length.

How is the logical address divided in segmentation?

The logical address is divided into two parts: the segment number (which identifies the segment) and the offset (which specifies the exact location within the segment). The segment number is used to find the segment in memory, and the offset is added to the base address to calculate the physical address.

What happens if the offset exceeds the segment size in segmentation?

If the offset (d) exceeds the segment size, it indicates an attempt to access data beyond the segment’s limit. This results in an error or trap, as the CPU cannot access memory outside the defined segment boundaries.

Can the size of segments vary in segmentation?

Yes, segments can vary in size based on the amount of code or data they contain. For example, a segment containing a small function may be smaller than one containing a large function or module.

How does segmentation improve memory management over paging?

Segmentation aligns memory allocation with the logical structure of the program, keeping related code in the same segment. This can reduce page faults and increase efficiency by keeping functions and modules intact, unlike paging, which divides the process into fixed-sized pages regardless of logical grouping.