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Problem of Fragmentation 📘

Memory Fragmentation

Memory fragmentation is a situation in the management of memory where memory space is wasted or rendered unusable due to the organization and allocation/deallocation mechanism. Despite having sufficient free memory, the system might still be unable to fulfill a memory request because the available

  • memory spaces are not contiguous and, thus, cannot be used together to satisfy the request.

Types of Fragmentation:

  • Internal Fragmentation:

    • Occurrence: It happens when memory is divided into fixed-sized blocks and allocated to processes. When a process gets a block of memory that is slightly larger than what it requested, the excess memory within the allocated block becomes unusable.
    • Example: An 8-byte block, rendered unusable after a split during a 10-byte memory request, becomes internally fragmented.

  • External Fragmentation:

    • Occurrence: It arises when free memory blocks are scattered, i.e., non-contiguous, thereby preventing their collective use to satisfy memory requests.
    • Example: Even though there might be two 16-byte blocks available (totaling 32 bytes), a 20-byte memory request can’t be satisfied if these blocks are non-contiguous.

size of metablock is 12 bytes.

🧐 Curiosity

  1. Question: What is the primary distinction between internal and external fragmentation? Answer: The main difference lies in their occurrence and impact on memory usability. Internal fragmentation refers to the wastage of memory within an allocated block due to allocating slightly more memory than required. On the other hand, external fragmentation happens when the system has enough free memory in non-contiguous blocks, making it unable to fulfill memory requests.

  2. Question: How does external fragmentation impact memory allocation strategies? Answer: External fragmentation makes memory allocation challenging and inefficient because even though there might be enough free memory collectively, the memory blocks are scattered and non-contiguous. As a result, memory requests cannot be fulfilled by combining these fragmented blocks, impacting system performance and memory utilization.

  3. Question: Can memory defragmentation resolve the issue of external fragmentation, and how? Answer: Yes, memory defragmentation can resolve external fragmentation by rearranging the memory blocks to place all free memory together, making it contiguous. This process may involve moving allocated memory blocks so that free blocks are consolidated into a single, larger block, thereby enabling it to satisfy larger memory requests.

  4. Question: How does internal fragmentation affect the efficiency of a memory management system? Answer: Internal fragmentation decreases the efficiency of a memory management system by creating unusable memory spaces within allocated blocks. This leads to memory wastage, as the unused spaces within blocks cannot be utilized by other processes, thereby reducing the overall effective available memory and potentially leading to the need for additional memory allocation, which could have been avoided.

  5. Question: How can memory management techniques minimize internal and external fragmentation? Answer: Memory management techniques, like using variable-sized partitions (to minimize internal fragmentation) or implementing algorithms such as Best Fit, Worst Fit, or First Fit (to minimize external fragmentation), can be employed. Utilizing paging or segmentation, which allows for physical and logical memory division, also helps in reducing fragmentation by managing memory in fixed-sized or variable-sized units, respectively.

🗣 Concepts in Simple Words

Memory Fragmentation 💽

Imagine you have a large shelf where you want to store boxes of different sizes. Over time, as you add and remove boxes, you notice that even though you have enough space on the shelf, it’s all in little gaps between the boxes, so you can’t fit a new, larger box. That's like memory fragmentation!

  • Internal Fragmentation: 📦 Imagine you have a box that is slightly bigger than the item you want to store in it. The little extra space in the box that is not being used is like internal fragmentation - it’s wasted space inside the allocated area.

  • External Fragmentation: 📏 Think of it as having enough space on your shelf but scattered in different places. Even if you add all these little spaces together, you can’t put a new box because the space isn't all in one place. This is like external fragmentation – having the memory you need but scattered in different spots, making it unusable for new, larger needs.

|----------------- HEAP MEMORY -----------------|
| _______   _______   _______   _______   _____|
||       | |       | |       | |       | |     ||
|| Proc1 | | FREE  | | Proc2 | | FREE  | |Pro..||
||_______| |_______| |_______| |_______| |_____||

|------- INTERNAL FRAGMENTATION in a Block -----|
| _______   _______   _______   _______   _____|
||       | |       | |       | |       | |     ||
|| Proc3 | |UNUSED | | Proc4 | |UNUSED | |Pro..||
||_______| |_______| |_______| |_______| |_____||

HEAP MEMORY:

  • Proc: Denotes processes that have been allocated memory.
  • FREE: Represents free memory blocks.
  • Note that despite having two free memory blocks, a process requiring a larger contiguous memory space than either of the two blocks cannot be allocated due to external fragmentation.

INTERNAL FRAGMENTATION:

  • Proc: Again represents allocated processes.
  • UNUSED: Indicates memory within an allocated block that cannot be utilized by the process and is therefore wasted, embodying internal fragmentation.