Memory Management in Operating Systems
Memory management is a vital function of an operating system (OS). It ensures that memory is allocated, used, and freed efficiently to support the execution of multiple programs. This article explains memory management concepts in a clear, beginner-friendly format using diagrams and real-world analogies.
📌 What Is Memory Management?
Memory management is the OS process responsible for managing primary memory (RAM). It ensures that applications and processes get the memory they need, prevents memory conflicts, and optimizes system performance.
📚 Logical vs. Physical Address Space
Just like a library uses a catalog (logical address) to find the physical shelf (physical address), a program uses logical addresses. The OS translates these into actual RAM addresses.
🧱 Contiguous and Non-Contiguous Allocation
In contiguous allocation, a single memory block is assigned to a process. Non-contiguous allocation, used in modern systems, breaks memory into parts, allowing flexible allocation to processes, avoiding fragmentation.
Single and Multiple Partition Allocation
- Single partition: All memory used by one program.
- Multiple partitions: Memory divided into chunks for multiple programs.
🔍 Fragmentation in Memory
Fragmentation happens when memory becomes scattered and unusable:
- Internal Fragmentation: Unused memory within an allocated block.
- External Fragmentation: Free memory split across the system, not usable as one block.
💻 Virtual Memory
Virtual memory allows a system to use disk space as an extension of RAM. This makes it possible to run large applications even with limited physical memory.
📄 Paging
Paging divides memory into fixed-size pages. It eliminates external fragmentation and improves memory usage. Pages are mapped from virtual memory to physical memory using a page table.
🔄 Demand Paging
Demand paging only loads memory pages when needed. If a page is not in RAM, a page fault occurs and the OS loads the page from disk, making efficient use of memory.
⚙️ Page Replacement Algorithms
When RAM is full, the OS must decide which page to remove. This is done using algorithms:
- FIFO: Replaces the oldest page.
- LRU: Replaces the least recently used page.
- Optimal: Replaces the page not used for the longest time in future.
📊 Memory Management Techniques
- Contiguous Allocation: Simple but causes fragmentation.
- Paging: Efficient and avoids external fragmentation.
- Segmentation: Divides programs into logical segments like stack, heap, etc.
📎 Summary
- Memory management ensures effective allocation and use of RAM.
- It includes techniques like paging, segmentation, and virtual memory.
- Efficient management prevents fragmentation and enhances performance.
