What are the different memory allocation techniques used in operating systems?

The different memory allocation techniques used in operating systems are:

1. Contiguous Memory Allocation: In this technique, the main memory is divided into fixed-sized partitions, and each process is allocated a contiguous block of memory. It is simple and efficient but suffers from external fragmentation.

2. Non-contiguous Memory Allocation: This technique allows memory allocation in non-contiguous blocks. It includes techniques like Paging and Segmentation.

3. Paging: In paging, the main memory and processes are divided into fixed-sized blocks called pages. The logical address space of a process is divided into fixed-sized blocks called page frames. It helps in reducing external fragmentation but may suffer from internal fragmentation.

4. Segmentation: In segmentation, the logical address space of a process is divided into variable-sized segments. Each segment represents a logical unit such as code, data, stack, etc. It helps in reducing external fragmentation but may suffer from internal fragmentation.

5. Virtual Memory: Virtual memory is a technique that allows processes to use more memory than physically available. It uses a combination of main memory and secondary storage (usually disk) to store and retrieve data. It provides benefits like increased memory capacity, protection, and sharing of memory.

6. Demand Paging: Demand paging is a technique used in virtual memory systems where pages are loaded into memory only when they are demanded by the process. It helps in reducing the initial memory requirement and improves overall system performance.

7. Swapping: Swapping is a technique where entire processes are moved in and out of main memory to the secondary storage. It is used when the system does not have enough memory to hold all the processes.

These memory allocation techniques are used by operating systems to efficiently manage and allocate memory resources to processes.