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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 ?
Effects of sleep deprivation and sleep fragmentation on upper airway collapsibility in normal subjects.
Further, such longitudinal prospective studies, with full polysomnography, are required to address whether the relationship between sleep apnea and risk for dementia and cognitive decline in patients with TBI is mediated by the sleep-apnea associated hypoxia or sleep fragmentation or moderated by characteristics of the TBI itself, such as severity and duration since onset.
Sleep fragmentation, sleep architecture and sleep duration were similar for all three ventilator modes as the difference between the modes for the 15 subjects were not statistically different.
In OSA, sleep fragmentation and intermittent hypoxia appear to induce elevated sympathetic nervous system activity, altered hypothalamic pituitary adrenocortical axis function as well as increased oxidative stress and activation of inflammatory pathways.
Postulated mechanisms have included hypoxaemia and sleep fragmentation, and treatment has been shown to reduce sleepiness while improving mood disturbances, cognition, and performance.
Often, this results in frequent awakenings that result in sleep fragmentation and discontinued use.
Sleep fragmentation has been identified as common among RA patients and may be worse when they have flares of disease.
Other historic facts supporting a diagnosis of narcolepsy include sleep fragmentation or disturbed nocturnal sleep, sleep paralysis, hypnagogic hallucinations, and family history.
The consequences of OSAS include excessive daytime sleepiness, secondary to sleep fragmentation, and cardiovascular derangements that are manifested as hypoxemia, increased negative intrathoracic pressure, and autonomic nervous system alterations.
Noise and nursing care--especially that related to incontinence--cause substantial sleep fragmentation in a population already attempting to adjust to the changes in sleep habits associated with aging.
Sleep fragmentation was defined using an index of the number of sleep stage transitions per hour of sleep.
Triggers for Somnabulism, such as sleep fragmentation and increased depth and/or duration of slow wave sleep, are also similar as that of other arousal disorders.