Efficient allocation and management of memory resources in computer systems
Memory management techniques are fundamental in computer systems to efficiently allocate and manage memory resources. These techniques ensure that processes have the memory they need to execute while maximizing the utilization of available memory.
Effective memory management is crucial for system performance and stability
Memory allocation strategies determine how memory is assigned to processes. The two main approaches are contiguous and non-contiguous allocation, each with its own advantages and disadvantages.
Allocates a single contiguous block of memory to a process
Allocates memory to a process in multiple non-contiguous blocks
Contiguous allocation assigns a single contiguous block of memory to a process. This approach is simple to implement but can lead to fragmentation issues.
Allocates a contiguous block of memory to a process. Typically used in systems with fixed-size partitions or with dynamic partitioning where a large enough contiguous block is available.
Requires finding a memory block large enough to accommodate the entire process. Memory manager keeps track of free and allocated blocks.
Non-contiguous allocation allows a process to be divided into multiple parts that can be placed in non-contiguous memory locations. This approach reduces fragmentation but requires more complex management.
Allocates memory to a process in non-contiguous blocks. Includes paging and segmentation techniques.
Requires paging or segmentation hardware support. Uses page tables or segment tables to keep track of memory locations.
Fragmentation in memory management refers to the inefficient use of memory space, resulting in wastage or fragmentation of available memory. There are two main types of fragmentation: internal fragmentation and external fragmentation, each requiring specific management techniques.
Occurs when allocated memory space is larger than what is actually needed by the process
Occurs when there is enough total memory space to satisfy a request, but it is fragmented into small, non-contiguous blocks
Internal fragmentation occurs when allocated memory space is larger than what is actually needed by the process. This results in wasted space within allocated memory blocks.
When memory is allocated in fixed-size blocks and a process does not fully utilize the entire block. For example, if a process needs 1KB but is allocated a 2KB block, 1KB is wasted.
When variable-sized allocations result in leftover space due to alignment requirements or memory allocation policies. Even with dynamic sizing, perfect matches are rare.
Best Fit, Worst Fit, First Fit: These allocation strategies aim to reduce internal fragmentation by matching process size closely to the available memory block size. For example, Best Fit allocates the smallest block that fits the process, minimizing leftover internal fragmentation.
In systems with dynamic partitioning, memory compaction involves rearranging memory contents to place all free memory together, allowing larger contiguous blocks to be allocated to processes.
| Strategy | Description | Effect on Fragmentation |
|---|---|---|
| First Fit | Allocates first available block that fits | May create more fragmented memory |
| Best Fit | Allocates smallest block that fits | Reduces internal fragmentation |
| Worst Fit | Allocates largest available block | May create many small unusable blocks |
External fragmentation occurs when there is enough total memory space to satisfy a request, but it is fragmented into small, non-contiguous blocks, making it unusable for allocation.
Total free memory might be sufficient, but no single contiguous block is large enough
Frequent allocation and deallocation of memory lead to small holes (free blocks) scattered throughout memory. As processes start and stop, memory becomes fragmented.
As processes finish and free memory, the remaining memory may be fragmented into small pieces that cannot be used efficiently. The freed blocks are often smaller than new allocation requests.
Similar to managing internal fragmentation, memory compaction involves rearranging memory to place all free blocks together, reducing external fragmentation and making larger contiguous blocks available for allocation.
Allocates memory in powers of two sizes. When a block is freed, it checks if its buddy (adjacent free block of the same size) is also free. If so, it merges them into a larger block, reducing fragmentation.
Techniques used in virtual memory systems where memory is divided into fixed-size pages or variable-sized segments. Paging reduces external fragmentation by allocating memory in fixed-size pages, while segmentation allows for more flexible allocation but requires management of segment tables to handle fragmentation.
Memory is allocated in powers of two and can be split/merged as needed