22516 Operating System Unit 5 Notes PDF

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                              Memory management is a crucial function of the operating system, ensuring optimal utilization of the computer's primary memory, or RAM (Random Access Memory). It's responsible for managing both the physical and logical aspects of memory.

 

Functions of Memory Management:

1. Process Isolation: Ensure that each process runs in its own memory space, preventing it from affecting another process unintentionally.
2. Automatic Allocation & Management: Efficiently and dynamically allocate memory as needed, and reclaim it when not in use.
3. Support for Modular Programming: Allow programs to be broken into smaller pieces or modules.
4. Protection & Access Control: Ensure that a process can't access memory locations that haven't been allocated to it.
5. Long-term Storage: Some memory contents need to be kept for prolonged periods, even beyond a power cycle.

 

Key Concepts & Techniques:

1. Contiguous Memory Allocation: Assigning a single contiguous block of memory to a process. This method often leads to fragmentation.
• Fragmentation:
• Internal Fragmentation: Memory gets wasted inside the allocated region due to block size allocation discrepancies.
• External Fragmentation: Free memory blocks are separated by allocated blocks, leading to scattered unusable memory chunks.
2. Paging: Memory is divided into small fixed-sized blocks called pages. When a process needs to be executed, its pages are loaded into any available memory frames, not necessarily contiguous. This technique helps to eliminate external fragmentation.
3. Segmentation: Memory is divided into variable-sized blocks based on the different segments of a program (like data, code, stack). Each segment is loaded into memory whenever needed. This method can still experience external fragmentation.
4. Virtual Memory: An abstraction that provides an "idealized abstraction of the storage resources that are actually available on a given machine." It allows processes to execute even if they're partially in primary memory. Techniques:
• Demand Paging: Only the required pages of a process are loaded, and others are loaded as needed.
• Page Replacement Algorithms: Determine which page to replace when a new page needs to be loaded into memory (e.g., LRU - Least Recently Used).
• Swapping: Moving processes in and out of memory to the backing store (usually a disk).
5. Memory Allocation Strategies:
• First Fit: Allocate the first available block of memory that's large enough.
• Best Fit: Allocate the smallest available block of memory that's large enough. This can lead to maximum external fragmentation.
• Worst Fit: Allocate the largest available block of memory. Assumes that the process will grow in the future.
6. Memory Protection: Utilizing registers to define the start and end of allocated memory, ensuring one process doesn’t overwrite the memory of another.

 

Conclusion:

Memory management in operating systems ensures efficient utilization of the computer's primary memory. Proper memory management ensures that processes run smoothly, efficiently, and without interfering with each other, leading to better system performance and stability.