Fixed size and variable size partitioning are two different approaches to memory management in computer systems, particularly in operating systems.
- Fixed Size Partitioning: Fixed size partitioning, also known as static partitioning, involves dividing the available memory into fixed-size partitions or blocks. Each partition has a specific size and can accommodate a single process. These partitions are typically created during system initialization and remain fixed throughout the system's operation.
In fixed size partitioning, when a process is loaded into memory, it is assigned to a partition that is large enough to accommodate it. If a partition is not large enough to hold a process, it remains unused. As a result, fixed size partitioning can lead to internal fragmentation, where memory is wasted due to the unused portion within a partition.
- Variable Size Partitioning: Variable size partitioning, also known as dynamic partitioning or dynamic memory allocation, involves dividing the available memory into variable-sized partitions based on the size of the incoming processes. The partitions are created and adjusted dynamically as processes are loaded and removed from memory.
In variable size partitioning, when a process is loaded, the system looks for a free partition that is large enough to hold the process. If there is no exact match, the system may allocate a slightly larger partition and split it into two, keeping one portion for the process and leaving the remaining portion as a new free partition. This splitting process can lead to external fragmentation, where free memory is scattered throughout the system in small chunks but cannot be used to accommodate larger processes.
Variable size partitioning helps in efficient memory utilization as it allows processes to occupy the exact amount of memory they require. However, it requires dynamic memory management algorithms to allocate and deallocate partitions effectively.
Overall, fixed size partitioning provides simplicity and predictable memory allocation, but it can waste memory due to internal fragmentation. Variable size partitioning offers better memory utilization but can suffer from external fragmentation. The choice between the two depends on the specific requirements and constraints of the system.