External sorting

External sorting is like sorting a bunch of toys by color but there are too many toys to fit in your toy box. So, you have to put some of the toys in a big box and store it outside your room. Now, you can only sort the toys that are inside your room, but you still want them all sorted by color.

To do this, you take a few toys at a time and put them in a smaller box, and keep doing this until you have boxes of toys that are all similar colors. Think of these smaller boxes as parts of the big box that is stored outside your room.

Once you have these smaller boxes, you can sort them by color, and then combine them back together to make one big sorted box of toys.

This is exactly how external sorting works. The toys are like data that needs to be sorted, and the toy boxes are like blocks of memory that are available for sorting. The large box outside the room is like a hard drive or memory that can store extra data that does not fit into the initial memory space.

To perform external sorting, you divide the data into smaller chunks based on the amount of memory available, sort each of these chunks in memory, and then store them back in the hard drive. Once all chunks are sorted, you merge them together to produce a fully sorted data set.

So external sorting is a process to sort data that cannot fit into memory entirely, by dividing data into smaller chunks, sort each chunk and combine them back together to produce a fully sorted data set.