Segmented, Paged and Virtual Memory

Summary

This video explains two memory management techniques used by operating systems: segmented and paged memory. In a segmented system, programs are divided into segments, which can be swapped between RAM and disk as needed. However, fragmentation can occur, especially for larger processes. Paged memory, on the other hand, divides memory into fixed-size pages, which helps utilize space more efficiently, but may slow down access due to fragmentation. The video also touches on virtual memory and the concept of disk thrashing, where excessive swapping can degrade system performance. It concludes by comparing the advantages and disadvantages of each method and mentions hybrid systems that combine both techniques.

Takeaways

• 😀 Segmented memory management divides memory into segments, each corresponding to a process, and tracks the start location and size of each segment.
• 😀 When memory becomes full, inactive segments may be swapped out to disk (swap file) to free up space for new processes.
• 😀 In a segmented system, memory segments are atomic; either the entire segment is in RAM or none of it is.
• 😀 Segmented memory can lead to fragmentation, where free spaces between active segments may be too small to fit larger processes.
• 😀 Paged memory management divides memory into fixed-size blocks called pages, which can be non-contiguous in physical memory.
• 😀 In a paged memory system, when memory is full, pages are swapped between RAM and secondary storage (disk), using paging in and out to manage memory.
• 😀 Virtual memory supplements RAM with secondary storage, allowing more programs to run by swapping inactive pages out to disk.
• 😀 Excessive paging can lead to disk thrashing, where the system becomes slow due to constant swapping between RAM and disk.
• 😀 Segmented memory is faster in accessing entire blocks of code but suffers from fragmentation, making large processes harder to load into memory.
• 😀 Paged memory is more efficient in utilizing free memory but can result in fragmented processes, which may cause slower performance due to paging overhead.
• 😀 Some systems combine segmented and paged memory management, using segments made of fixed-size blocks to leverage the benefits of both systems.

Q & A

What is the main concept behind segmented memory management?

Segmented memory management divides a program into different segments, each representing a logical unit like procedures or functions. These segments are loaded into physical memory, and the operating system manages them by swapping segments between memory and secondary storage when needed.

How does a computer handle the memory when multiple applications are launched?

When multiple applications are launched, the operating system manages memory by swapping segments in and out of RAM. If RAM fills up, idle processes or segments are moved to disk to make room for new applications, ensuring the system keeps running efficiently.

What is the role of a swap file in segmented memory management?

A swap file on the hard drive temporarily stores segments of processes that are not actively in use, allowing the system to free up memory for other processes. This ensures that the computer can handle more applications even when physical memory is limited.

Why are segments in a segmented memory system considered atomic?

Segments in a segmented memory system are atomic because they are indivisible; either the entire segment is in memory, or none of it is. This prevents partial loading of segments into memory and ensures consistency in program execution.

What are the disadvantages of a segmented memory system?

One major disadvantage of a segmented memory system is fragmentation, where free memory space becomes scattered in small gaps between segments. This can make it difficult to allocate larger segments, leading to inefficient use of memory.

What is the difference between segmented memory and paged memory?

In segmented memory, a program is divided into segments of varying sizes, whereas in paged memory, the program is divided into fixed-size pages. Segmented memory may lead to fragmentation, while paged memory handles fragmentation more efficiently by using smaller, uniform pages.

What happens during disk thrashing in a virtual memory system?

Disk thrashing occurs when the system spends too much time swapping data between physical memory and secondary storage, resulting in severe performance degradation. This happens when the system is overloaded and memory usage is inefficient.

How does virtual memory work in a paged memory system?

In a paged memory system, virtual memory allows the operating system to use secondary storage as an extension of RAM. Pages that are not actively in use are moved to disk, and when needed, they are paged back into RAM, enabling the system to run larger applications than the physical memory can accommodate.

Why might a system using paged memory perform more slowly compared to one using segmented memory?

Paged memory can lead to fragmented processes, where parts of a program are scattered across different pages in memory. This fragmentation can cause slower access to program data and result in decreased performance. In contrast, segmented memory offers faster access since entire blocks of code are loaded together.

What are the advantages of using hybrid memory management, combining both paged and segmented systems?

A hybrid memory management system combines the benefits of both segmented and paged memory. Each segment consists of several fixed-size blocks, which allows for better use of memory space while avoiding fragmentation and providing faster access to program code. This hybrid approach can optimize both memory usage and performance.