Re: the screen grab illustrating this article
The screenshot was from the book Illustrating BASIC written in 1977 by my late father Donald Alcock. Back in the day, one of the key problems that computers were used for was engineering, specifically finite state analysis of columns, beams and slabs. The key tools programmers used to attack this were vectors (or array), the matrix and its cousin the tensor, and these concepts were therefore implemented in the languages of this era, Fortran and BASIC. The MAT READ statement you see is for reading a matrix data structure into memory. DATA was used for populating an array.
I remember, as I grew up, we discussed the compatibility issues of the multiple versions of BASIC and what he decided to include in the book - it was a very difficult decision. Anyway, this is what he wrote in the Preface:
"There is soon to be a standard for "Minimal BASIC" by the American National Standards Institute (ANSI X3J2), and "Specification for Standard BASIC" by Bull, Freeman & Garland has been published by the National Computing Centre, UK (1973). These have not yet had time to encourage everyone to fall into line, so the BASIC that you meet will probably not be standard. I have accepted this as a fact of life, and, in writing this book, kept at my side ELEVEN manuals - each defining a different BASIC. Four of these versions are available on big computers operated by international "time-sharing" services; the other seven on computers ranging from big to "desk-top". From these eleven manuals I have tried to discover and point out where BASICs commonly differ from one another and recommend ways of avoiding dependence on any one particular version. I have used the word "portable" to describe a BASIC program written with independence in mind - and treat the need for portability as an axiom".
At the time, as a civil engineer, he was writing an engineering-oriented OS that ran on a Ferranti (later ICL) minicomputer and so had access to a more fully implemented version of BASIC that implemented matrices.
Regarding compatibility and standards: Argh! it's amazing how little has changed over the years - I'm looking at you SQL.