Nearly 30 years ago I wrote a best-selling computer book published by Ziff-Davis Press. It was an "expert" level book for programmers using compiled BASIC under DOS. Some of these programmers still exist! A wonderful lady in Canada spent six months re-creating my book as a PDF file for free download, and it''s now available on my web site. Scroll down to the link for BTU_BOOK.PDF: https://ethanwiner.com/fullmoon.html You'll notice on the same page above that all Crescent Software products are now in the public domain and are available for free download. DOS may be mostly dead, but the algorithms and concepts in the book are still useful. One of the coolest things in the book is a program that demonstrates the QuickSort sorting algorithm visually. For example, to sort customers by last name or purchases by date. There are many algorithms for sorting data, but QuickSort is the best because it requires the fewest steps. But its operation is difficult to visualize. So I ran the program and captured the screen to a video. The BASIC code shown at the beginning can be followed by anyone familiar with programming in other languages.