This online book assumes that you have installed and will be using J for Windows (Win31, Win95, or NT) or J for Macintosh. Any edition at Release 4 or later is appropriate.
There are minor differences in J for Macintosh, but they should not be a problem in using this book to learn J.
J for UNIX is not as directly usable with this book. The J language is identical, so the differences are all in areas such as how to edit text files. With a reasonable knowledge of UNIX and some extra effort this book can be used in learning J on a UNIX system. Some sections deal with facilities that are not part of J for UNIX and you will just have to read those sections without being able to execute the examples or experiment. In particular, J for UNIX does not have a plot facility or a form designer.