Internal and external fragmentation

Question

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

[filesystems] Internal and external fragmentation

Examples related to filesystems

Examples related to disk

Examples related to fragmentation