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Related to sleep fragmentation: polysomnography, polysomnogram


(computer science)
The tendency of files in disk storage to be divided up into many small areas scattered around the disk.
(cell and molecular biology)
Amitotic division; a type of asexual reproduction.
(mining engineering)
The blasting of coal, ore, or rock into pieces small enough to load, handle, and transport without the need for hand-breaking or secondary blasting.
Disordered behavior and mental processes.




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.

MS-DOS 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.


(1) See Android fragmentation.

(2) Storing data in non-contiguous areas on disk. As files are updated, new data are stored in available free space, which may not be contiguous. Fragmented files cause extra head movement, slowing disk accesses. A defragger program is used to rewrite and reorder all the files.

(3) In an IP network, breaking a data packet into smaller pieces in order to accommodate the maximum transmission unit of the network. See IP fragmentation.
References in periodicals archive ?
Ashley, "Acute sleep fragmentation induces tissue-specific changes in cytokine gene expression and increases serum corticosterone concentration," American Journal of Physiology--Regulatory, Integrative and Comparative Physiology, vol.
Acute medical illness is associated with greater sleep fragmentation, less TST and less SWS or REM sleep (26).
An alternate explanation is that apnea/hypopnea-associated sleep fragmentation, rather than hypoxia per se, negatively affects cognition.
Recent studies have substantiated this report, concluding that while there is significant individual variability in sleep patterns among residents, sleep fragmentation is generally severe, with many residents awake for long periods at night and asleep for substantial parts of the day.
Sleep fragmentation has been shown to lower patients' subjective assessments of wakefulness, mood, and attention.
Cammermeyer M: Sleep fragmentation of oxygen desaturation as etiology of cognitive disability with obstructive sleep apnea.
Sleep fragmentation in the elderly: relationship to daytime sleep tendency.
Habitual snoring may affect the snorer's health and performance during the day by causing the snorer to arouse or suffer sleep fragmentation (repetitive arousal from sleep); it is also a source of disturbance for the snorer's bed partner.
SDB children exhibit more EEG arousal, sleep fragmentation, sleep deprivation, daytime sleepiness, and attention-deficit disorders than that of children without SDB.
4) Experimental sleep fragmentation studies have demonstrated that in addition to duration, the quality and architecture of sleep may influence metabolism and body weight regulation.
Those OSA patients with more severe sleep fragmentation, nocturnal hypoxia, and abnormal sleep duration were significantly more likely to subsequently develop Alzheimer's disease than were OSA patients with less severely disrupted sleep measures, added Dr.
22] found reduced P300 amplitudes following a night of sleep fragmentation at some frontal, central, and temporal scalp sites but not over parietal areas where P300 is most prominent.