**From Rexx to AS/400**. Rexx is a portable language across platforms. For a proof look at links in

**Hall of fame**. In

**Introduction**I would like to show that Rexx is an interesting high-level programming language, too. This is an original introduction. I concentrate only on features of the language Rexx which are not included, in whole, in the others programming languages: arithmetic operations, work with words, the interpret instruction, the SOURCELINE function, multiple exits, associative and sparse arrays. I explain a further wonder in third part of the article

**From Rexx to AS/400**: i. e.

**External data queue**. We can't imagine numbers with a gigantic number of digits; we can't use these numbers. Hence I included in

**Arithmetic operations**the complete explanation of the arithmetic operations in the Rexx language. It is a good idea consider in the course of a solution of a numeric task that "Rexx computes in the same way as we do". Instructions do-(iterate, leave)-end, numeric, interpret, parse, built-in functions, compound variables, recursion, allow complex algorithms to be expressed in simple programs. Rexx is suitable for learning and teaching algorithmic programming, compiler construction, mathematic theory of computation (look at my simple implementation of the universal

**Turing machine**).