In terms of storing files on a computer, the data may be stored on different parts of the computer hard drive or disk. Computer data are stored in blocks that are ideally stored close to each other. When these data are stored apart from each other or at different areas in the storage disk, the data is said to be fragmented. The process of fragmentation literally refers to the inefficient storage of data blocks wherein they are placed in various parts of the computer storage disk. When there is fragmentation of data, the computer may take a longer time to retrieve certain elements and therefore data processing will also be longer than usual.

Computer fragmentation may either be internal or external. Internal fragmentation results from basic storage rules in terms of memory or space allocation in the storage disks. Under normal conditions, data is stored into different blocks or chunks. One chunk is able to store a specific number of bytes. When a particular data file is allocated with memory chunks, all maybe used even if some are not entirely full. This will result to some wastage in terms of storage space. The more empty chunks are used up, more fragmentation will occur. External fragmentation occurs when memory allocation is forced to split a particular data file into several chunks and place them apart because of existing memory that has already been allocated. This type of fragmentation happens when the storage algorithm cannot address the proper allocation of chunks in terms of size and location.

With data fragmentation, the computer will be affected in the sense that more time will be needed to process and/or retrieve data. Some applications will not be able to run as quickly and as smoothly as possible if corresponding data are fragmented in the storage disk. With this concern, the computer data may need to be defragmented to improve efficiency.