Internal and external fragmentation [closed]

Question

Can anyone please tell me the difference between internal and external fragmentation while allocation of disk space for files?

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Answer 1

External fragmentation
Total memory space is enough to satisfy a request or to reside a process in it, but it is not contiguous so it can not be used.

Internal fragmentation
Memory block assigned to process is bigger. Some portion of memory is left unused as it can not be used by another process.

Barron

Answer 2

First of all the term fragmentation cues there's an entity divided into parts — fragments.

• Internal fragmentation: Typical paper book is a collection of pages (text divided into pages). When a chapter's end isn't located at the end of page and new chapter starts from new page, there's a gap between those chapters and it's a waste of space — a chunk (page for a book) has unused space inside (internally) — "white space"

• External fragmentation: Say you have a paper diary and you didn't write your thoughts sequentially page after page, but, rather randomly. You might end up with a situation when you'd want to write 3 pages in row, but you can't since there're no 3 clean pages one-by-one, you might have 15 clean pages in the diary totally, but they're not contiguous

Orange

this is an amazing analogy to relate with. – Rubberize

Incredible analogy! Probably never going to forget this concept, thanks to this. – Teresa

Just wow. For this analogy... – Kirbee

Answer 3

I am an operating system that only allocates you memory in 10mb partitions.

Internal Fragmentation

• You ask for 17mb of memory
• I give you 20mb of memory

Fulfilling this request has just led to 3mb of internal fragmentation.

External Fragmentation

• You ask for 20mb of memory
• I give you 20mb of memory
• The 20mb of memory that I give you is not immediately contiguous next to another existing piece of allocated memory. In so handing you this memory, I have "split" a single unallocated space into two spaces.

Fulfilling this request has just led to external fragmentation

Tush

Answer 4

Presumably from this site:

Internal Fragmentation Internal fragmentation occurs when the memory allocator leaves extra space empty inside of a block of memory that has been allocated for a client. This usually happens because the processor’s design stipulates that memory must be cut into blocks of certain sizes -- for example, blocks may be required to be evenly be divided by four, eight or 16 bytes. When this occurs, a client that needs 57 bytes of memory, for example, may be allocated a block that contains 60 bytes, or even 64. The extra bytes that the client doesn’t need go to waste, and over time these tiny chunks of unused memory can build up and create large quantities of memory that can’t be put to use by the allocator. Because all of these useless bytes are inside larger memory blocks, the fragmentation is considered internal.

External Fragmentation External fragmentation happens when the memory allocator leaves sections of unused memory blocks between portions of allocated memory. For example, if several memory blocks are allocated in a continuous line but one of the middle blocks in the line is freed (perhaps because the process that was using that block of memory stopped running), the free block is fragmented. The block is still available for use by the allocator later if there’s a need for memory that fits in that block, but the block is now unusable for larger memory needs. It cannot be lumped back in with the total free memory available to the system, as total memory must be contiguous for it to be useable for larger tasks. In this way, entire sections of free memory can end up isolated from the whole that are often too small for significant use, which creates an overall reduction of free memory that over time can lead to a lack of available memory for key tasks.

Cleliaclellan

Maddy, you seem to have copied this text from another site, probably this one. If you do that, at minimum, you're required to add a link back to the site, indicating where you copied it from. I've done that for you here. This is still a borderline answer, though - in the future, please use information like this as the basis for an answer you write yourself, not as the entire answer. – Eisele