Retrieval of information is made simpler when it is stored into some predefined order. Therefore, Sorting is a very important computer application activity. Several sorting algorithms are obtainable. Different environments need different sorting methods. Sorting algorithms can be characterized into the following two manners:
A. Simple algorithms that require the order of n2 (written as O(n2))comparisons to sort n items.
B. Sophisticated algorithms which require the O(nlog2n) comparisons to sort n items.
The difference lies in the fact that the first method moves data merely over small distances in the procedure of sorting, whereas the second method moves data onto large distances, so that items settle in the proper order sooner, therefore resulting in fewer comparisons. Performance of sorting algorithm can also based on the degree of order already present in the data.
There are two fundamental categories of sorting methods: Internal Sorting & External Sorting. Internal sorting is applied whereas the entire collection of data is to be sorted is small adequate so that the sorting can occur within the main memory. The time needed to read or write is not assumed to be important in evaluating the performance of internal sorting methods. External sorting methods are applied on larger collection of data that reside on secondary devices. Read & write access times are a major concern in determining sorting performances of such methods.