External sort

Okay kiddo, let's talk about external sort. Imagine you're playing with a bunch of blocks but you have too many of them to play with at once. You need to sort the blocks so you can put them in their correct place, but you can only pick up a few blocks at a time. That's what external sort is like.

When we're working with a lot of data (like blocks), we can't sort all of it at once because the computer's memory isn't big enough. So instead, we sort small portions of the data at a time and then put those sorted pieces together into one big sorted piece.

Imagine we have a big pile of blocks, and we can only pick up 5 blocks at a time. We'll take those 5 blocks, sort them from smallest to largest, and put them in a smaller pile. We'll keep doing this until all the blocks are sorted into small piles.

But we're not done yet. We still have all these small piles of sorted blocks. We need to put them together into one big pile of sorted blocks. So, we'll take one block from each small pile and put them in order, then take another block from each pile and put them in order, and so on. Eventually, we'll have one big pile of sorted blocks.

That's basically how external sort works - we break down the data into smaller pieces that we can sort, and then we merge those sorted pieces into one big, sorted piece.