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Memory Management Introduction

Introduction

Memory management is a crucial function of the operating system (OS) that handles the allocation and deallocation of memory for processes. It ensures efficient utilization of RAM (Random Access Memory) while maintaining system performance and stability.

Objectives of Memory Management

✔ Allocate and deallocate memory dynamically for processes.
✔ Optimize memory usage to maximize system performance.
✔ Ensure process isolation to prevent unauthorized access.
✔ Enable multiprogramming by allowing multiple processes to run simultaneously.
✔ Support virtual memory to extend RAM using disk storage.

Memory Management Functions in OS

1. Process Address Space

Every process has a logical address space, which the OS maps to physical memory. It consists of:

  • Text (Code) Segment – Stores program instructions.
  • Data Segment – Stores global and static variables.
  • Heap Segment – Used for dynamic memory allocation.
  • Stack Segment – Stores function calls, local variables, and return addresses.

2. Memory Allocation

The OS assigns memory to processes in two ways:

  • Contiguous Memory Allocation – Fixed-size memory blocks assigned in a continuous manner.
  • Non-Contiguous Memory Allocation – Processes are allocated memory in separate locations (e.g., paging, segmentation).

3. Address Binding

Translates logical addresses to physical addresses at different stages:

  • Compile-time binding → Fixed memory address assigned during compilation.
  • Load-time binding → Memory address assigned when the program is loaded.
  • Execution-time binding → Memory can be dynamically allocated while running.

4. Swapping

The OS temporarily moves processes from RAM to disk when memory is full and loads them back when required.

5. Virtual Memory Management

Virtual memory allows a system to execute larger programs than physical RAM using disk space as an extension.

Memory Management Techniques

1. Contiguous Memory Allocation

  • Single Partition Allocation – Entire memory allocated to one process.
  • Multiple Partition Allocation – Memory divided into fixed or dynamic partitions.

Issues with Contiguous Allocation:

✔ Simple but ❌ leads to fragmentation.

2. Paging (Non-Contiguous Allocation)

  • Memory is divided into fixed-size pages.
  • The process is divided into equal-sized page frames.
  • The OS maintains a page table to map logical to physical addresses.

✔ Removes fragmentation but ❌ requires extra storage for page tables.

3. Segmentation

  • Divides memory into variable-sized segments based on logical divisions (e.g., functions, arrays).
  • Each segment has a base and limit in the segment table.

✔ Efficient for modular programming but ❌ prone to fragmentation.

Memory Management Challenges

✖ Fragmentation – Unused memory blocks waste space.
✖ Thrashing – Excessive swapping reduces performance.
✖ Security – Preventing unauthorized memory access.
✖ Overhead – Managing page tables and memory allocations consumes resources.

Conclusion

Memory management plays a vital role in ensuring efficient system performance by allocating and managing memory dynamically. Techniques like paging, segmentation, and virtual memory help overcome memory limitations, improving multiprogramming and system stability.