Operating System
Memory Management
Memory Management is one of the most important functions of an Operating System. It is responsible for managing primary memory (RAM), allocating memory to processes, tracking memory usage, and ensuring efficient utilization of system resources.
Since multiple programs run simultaneously in modern systems, memory management helps prevent conflicts between processes while improving speed, multitasking, and overall performance.
Need for Memory Management
- Efficient utilization of main memory
- Proper allocation and deallocation of memory
- Protection between processes
- Support for multitasking
- Faster execution of programs
Memory Hierarchy
Computer systems use different types of memory organized in a hierarchy based on speed, cost, and storage capacity.
Memory Hierarchy
Contiguous Memory Allocation
In contiguous memory allocation, each process occupies a single continuous block of memory.
- Simple and easy to implement
- Fast memory access
- Can lead to fragmentation problems
Fragmentation
Fragmentation occurs when memory becomes inefficiently used.
Internal Fragmentation
Wasted memory inside allocated partition.
External Fragmentation
Free memory exists but not in contiguous form.
Paging
Paging is a memory management technique where processes are divided into fixed-size pages and memory is divided into frames.
- Eliminates external fragmentation
- Allows non-contiguous memory allocation
- Uses page tables for mapping
Paging Structure
Process Pages
Memory Frames
Segmentation
Segmentation divides programs into logical units such as functions, arrays, or modules.
- Supports logical program structure
- Segment sizes can vary
- Easier sharing and protection
Virtual Memory
Virtual memory allows execution of programs larger than physical memory by using disk storage as an extension of RAM.
- Increases multiprogramming
- Improves memory utilization
- Uses demand paging technique
Page Replacement Algorithms
When memory becomes full, Operating Systems replace existing pages to load new pages.
| Algorithm | Description |
|---|---|
| FIFO | Replaces oldest page first |
| LRU | Replaces least recently used page |
| Optimal | Replaces page not needed for longest future time |
Thrashing
Thrashing occurs when the system spends more time swapping pages between RAM and disk instead of executing processes.
- Causes severe performance degradation
- Happens when insufficient frames are allocated
- High paging activity indicates thrashing
Paging vs Segmentation
| Paging | Segmentation |
|---|---|
| Fixed size memory blocks | Variable size logical units |
| Eliminates external fragmentation | May suffer external fragmentation |
| Hardware oriented | User/program oriented |
Summary
Memory Management is essential for efficient execution of modern operating systems. Techniques such as paging, segmentation, virtual memory, and page replacement help improve performance, multitasking, and resource utilization while ensuring smooth execution of processes.
Ready to test your Chapter VI: Memory Management knowledge?
Chapter VI: Memory Management
Test your understanding of memory hierarchy, paging, segmentation, virtual memory, page replacement algorithms, and thrashing.