fragment ==>
fragmentation definition
1. <networking> segmentation.
2. The process, or result, of splitting a large area of free
memory (on disk or in main memory) into smaller non-contiguous
blocks. This happens after many blocks have been allocated
and freed. For example, if there is 3 kilobytes of free space
and two 1k blocks are allocated and then the first one (at the
lowest address) is freed, then there will be 2k of free space
split between the two 1k blocks. The maximum size block that
could then be allocated would be 1k, even though there was 2k
free. The solution is to "compact" the free space by moving
the allocated blocks to one end (and thus the free space to
the other).
As modern file systems are used and files are deleted and
created, the total free space becomes split into smaller
non-contiguous blocks (composed of "clusters" or "sectors"
or some other unit of allocation). Eventually new files being
created, and old files being extended, cannot be stored each
in a single contiguous block but become scattered across the
file system. This degrades performance as multiple seek
operations are required to access a single fragmented file.
Defragmenting consolidates each existing file and the free
space into a continuous group of sectors. Access speed will
be improved due to reduced seeking.
The rate of fragmentation depends on the algorithm used to
allocate space and the number and position of free sectors. A
nearly-full file system will fragment more quickly.
MSDOS and Microsoft Windows use the simplest algorithm to
allocate free clusters and so fragmentation occurs quickly. A
disk should be defragmented before fragmentation reaches 10%.
See garbage collection.
(1997-08-29)
Nearby terms:
FRAD « fragile « fragment « fragmentation » FRAM » frame » frame buffer
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