SORTING a list of items — that is, arranging the items into increasing or decreasing order — is a common operation. It is also the most common example in the “analysis of algorithms,” which is the study of computational procedures and of the amount of time and memory that they require. The xSortLab applet knows five different sorting methods. It has a visual sorting mode, where you can watch as sixteen bars are sorted into increasing order. And it has a timed mode, where you can measure the time it takes to sort a large number of items. The applet is easy to use (but you probably won’t quite get the point of it unless you already know something about sorting).