ABL(ID:2955/abl001)Atlas Basic Languagefor Atlas Basic Language extended assembler for the Atlas computer References: PREFACE This manual supersedes the manual CS 348, "The Atlas Provisional Programming Manual", January 1963. It provides information for the programming of the Atlas 1 computer in the language known as Atlas Basic Language (ABL), It is a self-contained document, providing sufficient information about the Atlas 1 computer to enable programmers to write and develop programs in ABL without recourse to any other documents about Atlas 1. The Atlas 1 Computer is the latest result of a long-standing collaboration between Manchester University and Ferranti Ltd, A later version of the computer, known as Atlas 2, has been developed jointly by Cambridge University and Ferranti Ltd. In September 1963 the Computer Department of Ferranti Ltd., was acquired by I.C.T. Ltd., who now manufacture and market the Atlas computers. Atlas Basic Language (ABL) is a symbolic input language close to "machine language". Each ABL instruction corresponds to one machine instruction, and each part of an ABL instruction to each part of a machine instruction. In its simplest form an ABL instruction consists of four numbers corresponding exactly to the internal machine representation, but extensive facilities are also provided in ABL for the use of a variety of parameters and symbolic expressions which are evaluated by the ABL compiler. ABL also provides a comprehensive system of directives to control the assembly of a complete program. Finally ALL provides facilities for the input, conversion and storage of fixed-point numbers, floating-point numbers and character strings for use by the program. In this manual no attempt is normally made to differentiate between those facilities which are a basic part of the machine (e.g. the instruction repertoire) and those which are a part of the particular language ABL (e»g. the formats for writing instructions). This is partly because it is impossible to separate them completely -- any feature of the machine itself needs a language in which to describe it, and in this case that language is ABL - and partly because it is not normally necessary or helpful for a programmer to be conscious of the distinction* However, inasmuch as certain facilities of the machine itself are described here, parts of this manual are relevant and interesting to users of other Atlas programming languages. In particular, Chapter 1.0 "Preparing a Complete Program" applies to all Atlas languages. A word must be said about the enumeration of binary digits: throughout this manual the convention adopted is to number bits as 0, 1, 2 ...., starting always with bit number 0 at the more significant end. This convention differs from that used in documents on the Supervisor and in engineering documents, in which only the accumulator is numbered as here, and in all other cases bit 0 is the least-significant bit* External link: Online copy at ACL [321 programming languages with indication of the computer manufacturers, on whose machinery the appropriate languages are used to know. Register of the 74 computer companies; Sequence of the programming languages after the number of manufacturing firms, on whose plants the language is implemented; Sequence of the manufacturing firms after the number of used programming languages.] The exact number of all the programming languages still in use, and those which are no longer used, is unknown. Zemanek calls the abundance of programming languages and their many dialects a "language Babel". When a new programming language is developed, only its name is known at first and it takes a while before publications about it appear. For some languages, the only relevant literature stays inside the individual companies; some are reported on in papers and magazines; and only a few, such as ALGOL, BASIC, COBOL, FORTRAN, and PL/1, become known to a wider public through various text- and handbooks. The situation surrounding the application of these languages in many computer centers is a similar one. There are differing opinions on the concept "programming languages". What is called a programming language by some may be termed a program, a processor, or a generator by others. Since there are no sharp borderlines in the field of programming languages, works were considered here which deal with machine languages, assemblers, autocoders, syntax and compilers, processors and generators, as well as with general higher programming languages. The bibliography contains some 2,700 titles of books, magazines and essays for around 300 programming languages. However, as shown by the "Overview of Existing Programming Languages", there are more than 300 such languages. The "Overview" lists a total of 676 programming languages, but this is certainly incomplete. One author ' has already announced the "next 700 programming languages"; it is to be hoped the many users may be spared such a great variety for reasons of compatibility. The graphic representations (illustrations 1 & 2) show the development and proportion of the most widely-used programming languages, as measured by the number of publications listed here and by the number of computer manufacturers and software firms who have implemented the language in question. The illustrations show FORTRAN to be in the lead at the present time. PL/1 is advancing rapidly, although PL/1 compilers are not yet seen very often outside of IBM. Some experts believe PL/1 will replace even the widely-used languages such as FORTRAN, COBOL, and ALGOL.4) If this does occur, it will surely take some time - as shown by the chronological diagram (illustration 2) . It would be desirable from the user's point of view to reduce this language confusion down to the most advantageous languages. Those languages still maintained should incorporate the special facets and advantages of the otherwise superfluous languages. Obviously such demands are not in the interests of computer production firms, especially when one considers that a FORTRAN program can be executed on nearly all third-generation computers. The titles in this bibliography are organized alphabetically according to programming language, and within a language chronologically and again alphabetically within a given year. Preceding the first programming language in the alphabet, literature is listed on several languages, as are general papers on programming languages and on the theory of formal languages (AAA). As far as possible, the most of titles are based on autopsy. However, the bibliographical description of sone titles will not satisfy bibliography-documentation demands, since they are based on inaccurate information in various sources. Translation titles whose original titles could not be found through bibliographical research were not included. ' In view of the fact that nany libraries do not have the quoted papers, all magazine essays should have been listed with the volume, the year, issue number and the complete number of pages (e.g. pp. 721-783), so that interlibrary loans could take place with fast reader service. Unfortunately, these data were not always found. It is hoped that this bibliography will help the electronic data processing expert, and those who wish to select the appropriate programming language from the many available, to find a way through the language Babel. We wish to offer special thanks to Mr. Klaus G. Saur and the staff of Verlag Dokumentation for their publishing work. Graz / Austria, May, 1973 |