Since the end of the 1950s László Kalmár has been interested in the information technology. During a 20 years period he designed several variants of computers interpreting high-level programming languages on architectural levels

Makay, Árpád

English

Makay Árpád

University of Szeged

Acta Cybernetica 18 (2007) 9–14.The activities of László Kalmár in the world ofinformation technologyÁrpád Makay∗AbstractSince the end of the 1950s László Kalmár has been interested in the in-formation technology. During a 20 years period he designed several variantsof computers interpreting high-level programming languages on architecturallevels.Keywords: logical machine, formula-driven computer, high-level languageinterpreter machineTowards the end of the 1950s, information technology (IT) became one of thefields in which László Kalmár was highly interested. He was clearly aware of therapid spread of computers and their excellent applicability for numeral computa-tions. It is nevertheless extremely likely that the links between mathematics andIT were what caught his interest and shaped his views of this field. It is undoubtedthat he tackled problems from the aspect of a mathematician, always attempt-ing to apply mathematical methods in a world, which at that time was virtuallypurely technical and technological. It soon became obvious that IT requires andmakes wide use of the laws and methods of mathematics: it may suffice merelyto mention the inspiring role of automata theory or coding theory. The exactnessof mathematics is reflected in the problem solving of IT, the precise understand-ing of the problems and their detailed analysis, which often demands considerablework. Kalmár’s interdisciplinary knowledge played a significant role in his continu-ous search for new areas of use of IT, defining concrete problems for which he oftenfound solutions and attracted the interest of researchers and developers.It should be remembered that the freedom of researchers to carry out effec-tive work in Hungary in that period was restricted by a number of factors. Thetechnical resources in the country were rather poor. For understandable reasons,most of the resources were placed in the service of the economy and the runningof the state, only a minor part being made available for teaching and research.Kalmár’s wide-ranging contacts and (from the 1960s) his nationwide recognition inthe world of IT helped him overcome many of the technical obstacles, especially∗University of Szeged, Árpád tér 2, Szeged, Hungary.9brought to you by COREView metadata, citation and similar papers at core.ac.ukprovided by University of Szeged10 Árpád Makayin the practical teaching area. Nonetheless, the need to adapt to the external con-straints certainly influenced his thoughts and plans. One of the main areas of hisinterest, the combination programming languages and mathematics, and especiallythe formal language of logic, was restricted from the outset, the limitations beingset by his ambition for the availability of the necessary resources.Kalmár was unceasingly convinced that the already considerable developmentof the IT world could benefit still further from the innovative work of Hungarianresearchers. In consequence of his international reputation, the leading journals andtechnical books were at his disposal, often as complimentary copies. The world wasgenerally open to him. At conferences, he was able to meet internationally respectedresearchers and to set out his ideas and achievements. In this way he acquired up-to-date information on the areas of perspective research and development, whichhe readily shared with his students and colleagues.When an effective tool such as the computer becomes available to an individ-ual, his or her imagination suddenly catches wings. And this is what happened tothe early IT researchers, engineers and end-users in Hungary, among them LászlóKalmár. As an example, the machine translation of natural languages seemedattainable from the very beginning. Kalmár closely watched and supported theHungarian group working on this project. We now know that this goal was reachedin part only much later. For that group at that time, the objective appearedunattainable, though their activities furnished important information and knowl-edge relating to the field of linguistics.László Kalmár was no stranger to philosophy. Perhaps this was one of the rea-sons why he became interested in some of the unanswered questions of mathematicallogic which (with full mathematical exactness) touched on the limits of reliability ofmathematics. Questions often arose in IT (also referred to as cybernetics) such asthose concerning the relationship of man and a ”thinking” machine, the ability ofa machine to reproduce itself, and the controllability of computers. Kalmár devel-oped his own concepts of these issues and often put forward his ideas at appropriateforums. He did this mainly as a mathematician, a stranger to exaggeration andscience fiction.László Kalmár worked in the purely theoretical realm of mathematical logic;it may be stated that he was a real theoretical researcher. In the world of IT,however, he strived towards concrete instruments. The technology was limited, buthe designed tools that could be constructed.The first project that was achieved was a by-product of a departmental seminar.The theme was the technical implementation of mathematical logic (propositionallogic). This is an exciting topic if it is considered that the active parts of computersare logical circuits, the tasks of which are logical calculations. The decision wastaken to build a ”logical machine” that computes the values of logical formulae [1].The formula applied could contain a maximum of 8 variables, and all the basicoperators of calculus could be used. A double contact switch represented the valueof a variable or a component formula. One pole had the value TRUE, and the otherone the value FALSE. Accordingly, an operator of two variables needed two inputand one output switches. Special cables connected the poles. These connectionsThe activities of László Kalmár in the world of information technology 11had to be set according to the logical operators; it may be said that the operatorswere programmed. The input and output poles of the boxes, already programmedfor the basic operators, were appropriately connected to each other so that formulaeof desired length became computable. Operator priority and the use of parentheseswere enabled. It is obvious that the machine did not tackle the problem by reducingthe formula to some kind of normal form. The values of the maximum 8 operandswere set by a simple series of switches, their values and that of the formula beingindicated by lamps on the display.The logical machine was a demonstrative tool, but it led to a degree of self-confidence necessary for more difficult challenges to be tackled. Every creator feelsthe need to explain what his or her creation is good for: the formula built upfrom the boxes is a circuit that is being tested by the machine. This activity wassupported by a relayed ”memory”, together with the potential for the simultane-ous handling of a number of formulae. By 1959 the machine had received a newapplication (one necessary in most computers): it had become a binary adder.It was roughly at this time that the training of ”programming mathematicians”started at the University of Szeged, and these courses became increasingly morepopular. The characteristic features of the courses were very thorough trainingin mathematics and programming, first in assembly, and later in higher-level lan-guages. While providing several mathematical courses, László Kalmár was theprofessor of machine programming.In the 1960s, he experienced that programs written in assembly (or in directcode) were more effective than the codes generated by the compilers, not to mentionthe time and memory requirements of the compilation process. The effectivenesswas a result of the work of the programmer in searching for the memory and timeoptimum. He also observed that the programming work, i.e. the human energyinvested in problem solving, is more effective if a higher-level language is used. Thislatter is nowadays held to be of greatest importance. At that time, Kalmár couldnot predict that within 25 years the memory and computing capacity of computerswould have become virtually limitless, and that the abilities of compilers would havebeen enhanced considerably as a consequence of theoretical results. He believedthat the solution lay in the approach of machine code to the syntax and semanticsof higher-level languages.During his productive IT activities, Kalmár often returned to this idea of aformula-driven machine. The possibilities available in the various periods are re-flected by some of the versions planned throughout the years. In parallel, hisgoal was a definition of the computer as an algebraic structure, his plans beingconstructed on this precise theory. As an example, he looked upon a computeroperation as (amongst others) a transformation in the memory state. However,because of the large number and complexity of the operations, the characteristicsof this transformation could not be written with mathematical exactness. In orderfor this to be done, the model should have been brought into a much simpler level,e.g. to the level of Turing machine theory, but the practical demands did not allowthis. Accordingly, the algebraic model rather played the role of a general approachand was not used directly in the design.12 Árpád MakayThe first plans involved the use of the Ljapunov operational language inter-preter machine [2]. The language allowed the use of a limited number of variables,expressions built up with the applications of arithmetical operations, and a fewalgorithmic tools: conditional clauses and cycles. The syntax was straightforward.Lexical analysis was barely needed. Because of the lack of block structures andprogram segmentation, there was no need for the most difficult techniques appliedin modern interpreters, which at that time were probably impossible to implementwith the technical support available then.The computational unit of the machine was a stack-like structure built up fromregister quartets. These were designed to handle the arithmetical and logical oper-ations of two operands; they stored the two operands, the operation and (once thevalues of the operands were available) the result. The result register of the registerquartet was connected to both operand registers of the higher-level register quartetthrough gates. At most one of the gates was open, in order to receive the result ofthe operation computed at the lower level.The program was run through the sequential reading of the characters in onepass. At all times there was one active register quartet and one of its registers wasactive. In one step, the value (if any) of the next variable from the sequence wasplaced in the active register. In every step, the state of activation of the currentregister quartet and its register was refreshed, and the states of the gates were set.If the operation could be computed (both operands present in a register quartet),the operation was performed and the result flowed upwards through the open gate.An analysis of the system reveals that simple cycles can be implemented withthe described register hierarchy, since the repeating condition is also an expression.Apart from this, a control unit was needed, with the role of interpretation of thesequential, conditional and cyclic clauses. The memory assignments and the in-dexed variable handling demanded a special design. Kalmár’s plans included all ofthese features, but the result of prime importance was the technically applicable,special stack architecture. The conditions for the building of the machine could notbe met within Hungary, but parts of his machine plans were utilized in the MIRmachine of the Ukrainian Academy of Sciences, built in 1966.By the beginning of the 1960s, it was evident that the stack was an extremelypowerful tool in IT. If the traditional infix expressions were converted to postfixform and put into the stack, their interpretation was child’s play. The use of a stacksimplified the conversion too. If the algorithmic parts of programming languagessuch as ALGOL-60 could be converted to postfix form, then (by means of a one-pass compilation) the program could be run several times without being compiledin the classical machine language. This was more or less achieved, and extremelyefficient interpreters were developed on the basis of this theory. The efficiency wasfurther increased by building the stack into the hardware level of the architectureof the computer, together with the technique of microprogramming.In the meantime, theoretical results were obtained that gave a definitive direc-tion to the evolution of IT. The design of efficient lexical analysis algorithms wasbased on the theory of finite automata. The theory of pushdown automata and theirspecial classes defined the limits to be taken into consideration within the syntaxThe activities of László Kalmár in the world of information technology 13of programming languages for the building of efficient compilers and interpreters.The limitations were loose, and the requirements of the programmers concerningthe programming languages could therefore be fully satisfied. The main direction ofIT therefore became the use of high-level programming languages (supporting bothgeneral needs and special requirements) and the construction of efficient compilersand interpreters for them.In 1973, László Kalmár was requested by the Hungarian Academy of Sciences toexamine the situation regarding computers and higher-level programming languages(including machine languages) and the progress to be expected in these fields. Thegoal was for Hungarian IT to find its place and to play an appropriate role in thebright future of IT research and development. It was becoming increasingly moreobvious that, like all other countries in Eastern Europe, Hungary had failed torecognize the importance of IT in time, and had not allocated sufficient funds forIT research. This invitation was a sign of appreciation of the leader of one of thefew research groups which had been producing results and which had come up withconstructive ideas despite the inadequate support.The development of the various generations of computers up to that time, andthe methods of constructing computer architectures, were reviewed in a series ofmonographs [3]. Naturally, the emphasis was on programming languages and theirinterpretational possibilities, one of Kalmár’s main interests. In the final edition,some 15 years after the planning of the first formula-driven machine he put forwarda new proposal for a computer that could be programmed through the use of ahigh-level machine language.What were the challenges, to which the new plan was intended to respond?A look at the algorithmic (problem-oriented) languages reveals that the partsbuilding up the syntax have become clear, and new languages can be designed bycombining these parts at will. The block structure and the use of modules werenecessities. From the aspect of semantics, the notion of the expression had becomevery clear, mainly as a result of the increased number of data structures. The pro-grams themselves defined complex data types, and the classical sets of values couldno longer be used without appropriate care. The definition and implementationwere separated, a situation regarded as normal by today’s C++ or Java program-mer. It was now obvious that the handling of reference types needed extensiveredesigning, a feature applied earlier only for indexed variables and memory as-signments. It cannot be claimed that the new plan provided adequate answer toall these questions, but it did so for most of them.The technology too had been evolving. The problems involving the hardware-manipulated stack had been eliminated. The technique of microprogramming wasavailable, a tool that raised the programming level above that of the architecture.The implementation of a redesigned architecture with high-level machine languageagain seemed feasible.In the design stage, it became obvious to Kalmár that a single algorithmic lan-guage running on a given architecture could no longer satisfy the users. Compilerswere clearly needed. The suggested high-level language was designed to be close tomore general programming languages, particularly from the aspect of syntax. This14 Árpád Makaycould result in easier compiling, less human work, and lower hardware requirements.The research group led by Kalmár devised the proposed language. He did notdevelop a technical plan for the implementation of this language as he had earlierdone with the formula-driven machine. He hoped that the various Hungarian work-groups would share their knowledge and that his plans would materialize via suchcollaboration. In order to verify the language and prove its suitability, he suggestedsimulation methods. His research group did not lack the necessary knowledge, butthe simulator was not built. It is probable that Kalmár’s energy was wasted to someextent by his intent on publishing his conceptions in academic and technical circles.The reception was appropriate, and the observations were professional. However,it was at this time that Eastern Europe started planning great developments in thefield of IT, and Hungary did not want to be left behind; it therefore adapted to thetendencies determined by ”the greats”.What can be said today about formula-driven issues?Some 30 years ago, IT developed at a very rapid, but quite unexpected tempo.Economizing with hardware resources now belongs to the past; the pace is dictatedby the application needs. Many criticize this attitude. Not only has the lowestprogramming level not risen but it has even become lower, e.g. as a consequenceof the RISC technology. The need for the portability of applications over variousarchitectures has nevertheless given rise to a shared-language machine, the Javavirtual machine. This has taken place with a different objective and by differentmeans, but its roots are common with those of the formula-driven machine.References[1] L. Kalmár, A new principle of construction of logical machines, in Proceedingsof 2-e Congres Unternat. de Cybernetique, Namur (1958) 458-463. See in PDFform: http://www.inf.u-szeged.hu/kalmar2005/tcs/kalmar1958.pdf[2] L. Kalmár, On a digital computer which can be programmed in a mathemat-ical formula language, in Proceedings of 2nd Hungarian Congress of Mathe-matics, Budapest (1960) Vol. 5, 3-16. See in PDF form: http://www.inf.u-szeged.hu/kalmar2005/tcs/kalmar1960.pdf[3] Manuscript series under the title ”Belső gépi nyelvek”, Szeged (1973) (ed.:László Kalmár). Only available in Hungarian.Szeged, 10 December 2004

The activities of László Kalmár in the world of information technology

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The activities of László Kalmár in the world of information technology

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