The scattering of data over a disc caused by successive recording and deletion operations. Generally this will eventually result in slow data recall, a situation that is not acceptable for video recording or replay. The slowing is caused by the increased time needed to randomly access data. With such stores, defragmentation routines arrange the data (by copying from one part of the disc to another) so that it is accessible in the required order for replay. Clearly any change in replay, be it a transmission running order or the revision of an edit, could require further defragmentation.

True random access disc stores, able to play frames in any order at video rate, never need defragmentation.