CORREGATE(ID:391/cor014)Based on IT Related languages
References: At Carnegie Tech (now CMU) the 650 arrived in July 1956. Earlier in the spring I had accepted the directorship of a new computation center at Carnegie that was to be its cocoon. Joseph W. Smith, a mathematics graduate student at Purdue, also came to fill out the technical staff. A secretary-keypuncher, Peg Lester, and a Tech math grad student, Harold Van Zoeren, completed the staff later that summer. The complete annual budget -- computer, personnel, and supplies -- was $50,000. During the tenure of the 650, the center budget never exceeded $85,000. Before the arrival of the computer, a few graduate students and junior faculty in engineering and science had been granted evening access to a 650 at Mellon National Bank. In support of their research, the 650, largely programmed using the Wolontis-Bell Labs three-address interpreter system, proved invaluable. The success of their efforts was an important source of support for the newly established Computation Center. The 650 operated smoothly almost immediately. The machine was quite reliable. Even though only a one-shift maintenance contract was in force, by the start of fall classes the machine was being used on the second shift, as well as weekends. The talented user group, the stable machine, two superb software tools -- SOAP (Poley 1957) and Wolontis (see Technical Newsletter No. 11 in this issue) -- and an uninhibited open atmosphere contributed to make the center productive and, even more, an idea-charged focus on the campus for the burgeoning insights into the proper -- nay, inevitable -- role of the computer in education and research. Other than the usual financial constraints, the only limits were lack of time and assistance. The center was located in the basement of the Graduate School of Industrial Administration (GSIA). Its dean, Lee Bach, was an enthusiastic supporter of digital computation. Consequently, he was not alarmed at the explosion in the use of the center by his faculty and graduate students, and he acceded graciously to the pressure, when it came, to support the center in its requests to the administration for additional space and equipment. From its beginning the center, its staff, and many of the users were engaged in research on programming as well as with programming. So many problems were waiting to be solved whose programs we lacked the resources to write: We were linguistically inhibited, so that our programs were too often exercises in stuttering fueled by frustration. Before coming to Carnegie, Smith and I had already begun work on an algebraic language translator at Purdue intended for use on the ElectroData Datatron computer, and we were determined to continue the work at Carnegie. The 650 proved to be an excellent machine on which to pursue this development. Indeed, the translator was completed on the 650 well before the group at Purdue finished theirs. The 650 turned out to have three advantages over the Datatron for this particular programming task: punched cards being superior to paper tape, simplicity in handling alphanumerics, and SOAP. The latter was an absolutely crucial tool. Any large programming task is dominated by the utility with which its parts can be automatically assembled, modified, and reassembled. The translator, called IT for Internal Translator (see Perlis and Smith 1957), was completed shortly after Thanksgiving of 1956. In the galaxy of programming languages IT has become a star of lesser magnitude. IT'S technical constructs are of historical interest only, but its existence had enormous consequences. Languages invite traffic, and use compels development. Thus IT became the root of a tree of language and system developments whose most important consequence was the opening of universities to programming research. The 650, already popular in universities, could be used the way industry and government were soon to use FORTRAN, and education could turn its attention to the subject of programming over and above applications to the worlds of Newton and Einstein. The nature of programming awaited our thoughts. No other moment in my professional life has approached the dramatic intensity of our first IT compilation. The 650 accepted five cards (see Figure 1) and produced 42 cards of SOAP code (see Figure 2) evaluating a polynomial. The factor of 8 was a measure of magic, not the measure of a poor code generator. For me it was the latest in a sequence of amplifiers, the search for which exercises computation. The 650 implementation of IT had an elastic quality: it used 1998 of the 2000 words of 650 storage, no matter what new feature was added to the language. Later in 1957 IT-2 was made available and bypassed the need for SOAP completely. IT-2 translated the IT language directly into machine code. By the beginning of 1958 IT3 became available. It was identical to IT-2 except that all floating-point arithmetic was performed in double precision. For its needs GSIA produced IT-2- S which was IT-2 using scaled fixed-point arithmetic. The installation of the FORTRAN character set prompted the replacement of IT-9 by IT-2- A-S, which used both the FORTRAN character set and floating-point hardware. With IT-2-A-S the work on IT improvements came to an end at Carnegie. While the IT developments were being carried out within our Computation Center, parallel efforts were under way on our machine in the development of list-processing languages under the direction of Allen Newell and Herbert Simon. The IPL family and the IT family have no linguistic structure in common, but they benefited from each other's existence through the continual interaction of the people, problems, and ideas within each system. The use of Wolontis decreased. Soon almost all computation was in IT, and use expanded to three shifts. By the end of the summer of 1957, IT was in the hands of a number of other universities. Case and Michigan made their own improvements and GAT, developed by Michigan, became available in 1958 (see Arden and Graham 1958). It bypassed SOAP, producing machine code directly, and used arithmetic precedence. We were so impressed by GAT that we immediately embarked on its extension and produced GATE (GAT Extended) by spring of 1959. GATE was later transported to the Bendix G-20 when that computer replaced the 650 at Carnegie in 1961. The increased use of the machine and the increased dependence on IT and its successors as a programming medium pressured the computing center into continual machine expansion. As soon as IBM provided enhancements to the 650 that would improve the use of our programming tools, our machine absorbed them: the complete FORTRAN character set, index registers, floating point, 60 core registers, masking and format commands and, most important, a RAMAC disk unit. All but the last introduced trivial modifications to our language processors. There was the usual grumbling from some users because the enhancements pressured (not required) them to modify both the form and logic of their programs. The users were becoming computer-bound by choice as well as need, though, and they had learned the first, and most important, lesson of computer literacy: In man-machine symbioses it is the human who must adjust, adapt, and learn as the computer evolves along its own peculiar gradients. Getting involved with a computer is like having a cannibal as a valet. Most universities opted for magnetic tape as their secondary storage medium; Carnegie chose disks. Our concern with the improvement of the programming process had thrust upon us the question: How do programs come into being? Our answer: Pure reasoning and the artful combination of programs already available, understood, and poised for modification and execution. It is not enough to be able to write programs easily; one must be able to assemble new ones from old ones. Sooner or later everyone accepts this view -- first mechanized so admirably on the EDSAC almost 40 years ago (Wilkes, Wheeler, and Gill 1957). Looked at in hindsight, our concern with the process of assembly was an appreciation of the central role evolution plays in the man-computer dialogue: making things fit is a crucial part in making things work. It was obvious that retention and assembly of programs was more easily realized with disk than with tape. Like everything else associated with the 650, the RAMAC unit worked extremely well. Computation became completely dependent on it. GATE, our extension of GAT, made heavy use of the disk (Perks, Van Zoeren, and Evans 1959). Programs were getting larger, and a form of segmentation was needed. The assembly of machine-language programs and already compiled GATE programs into new ones was becoming a normal mode of use. GATE provided the vehicle for accomplishing these tasks. The construction of GATE was done by Van Zoeren and Smith. Not all programs originated in GATE; some were done in machine language. SOAP, always our model of a basic machine assembly language, had matured into SOAP 11 but had not developed into an adult assembler for a 650 with disks. IBM was about to stunt that species, so we designed and built TASS (Tech Assembly System). Smith and Arthur Evans wrote the code; Smith left Carnegie, and Evans completed TASS. A few months later he extended it to produce TASS I! and followed it with SUPERTASS. TASS and its successors were superb assemblers and critical to our programming research (Perks, Smith, and Evans 1959). Essentially, any TASS routine could be assembled and appended to the GATE subroutine library. These routines were relocatable. GATE programs were fashioned from independently compiled segments connected by link commands whose executions loaded new segments from disk. Unfortunately, we never implemented local variables in GATE, although their value was appreciated and an implementation was sketched. The TASS family represented our thoughts on the combinational issues of programming. In the TASS manual is the following list of desiderata for an assembler: 1. Programs should be constructed from the combination of units (called P routines in TASS) so that relationships between them are only those specified by the programmer. 2. A programmer should be able to combine freely P routines written elsewhere with his own. 3. Any program, once written, may become a P routine in the library. 4. When a P routine is used from the library, no detailed knowledge of its internal structure is required. 5. All of the features found in SOAP I! should be available in P routines. TASS supported an elaborate, but not rococo, mechanism for controlling circumstances when two symbols were (1) identical but required different addresses and (2) different but required identical addresses. Communication between P routines was possible both at assembly and at run time. Language extension through macrodefinitions was supported. SUPERTASS permitted nesting of macrocalls and P routine definition. Furthermore, SUPERTASS permitted interruptions of assembly by program execution and interruption of execution for the purpose of assembly. Many of the modern ideas on modularization and structured programming were anticipated in TASS more as logical extensions to programming than as good practice. As so often happens in life cycles, both TASS and GATE attained stable maturity about the time the decision to replace the 650 by the Bendix G-20 was made. Three other efforts to smooth the programming process developed as a result of the programming language work. IBM developed the FORTRANSIT system (see Hemmes in this issue) for translating FORTRAN programs into IT, thus providing a gradient for programs that would anticipate the one for computer acquisition. Van Zoeren (1959) developed a program GIF, under support of Gulf Oil Research, that went the other way so that programs written by their engineering department for their 650 could run on an available 704. Both programs were written in SOAP II. GATE translated programs in one pass, statement by statement. Van Zoeren quickly developed a processor called CORREGATE that enabled editing of compiled GATE programs by processing, compiling, and assembling into already compiled GATE programs only new statements. GATE was anticipating BASIC, although the interactive, time-sharing mode was far from our thoughts in those days. As so often happened, when a new computer arrived, sufficient software didn't. The 650 was replaced in the spring of 1961 by a superior computer, the Bendix G20, whose software was inferior to that in use on our 650. For a variety of reasons, it had been decided to port GATE to the new machine -- but no adequate assembly language existed in which to code GATE. TASS had become as complex as GATE and appeared to be an inappropriate vehicle to port to the new machine, particularly because of the enormous differences in instruction architecture between the two machines. Consequently, a new assembler, THAT (To Help Assemble Translators) was designed (Jensen 1961). It was a minimal assembler and never attained the sophistication of TASS -- another example of the nonmonotonicity of software and hardware development over time. We found an important lesson in this first transition. In the design and construction of software systems, you learn more from a study of the consequences of success than from analysis of failure. The former uses evolution to expose necessary revolution; the latter too often invokes the minimal backtrack. But who gave serious attention to the issues of portability in those days? The 650 was a small computer, and its software, while dense in function, was similarly small in code size. The porting of GATE to the G-20 was accomplished in less than one man-year by three superb programmers, Evans, Van Zoeren, and Jorn Jensen, a visitor from the Danish Regnecentralen. They shared an office, each being the vertex of a triangle, and cooperated in the coding venture: Jensen was defining and writing THAT, Evans was writing the lexical analyzer and parser, and Van Zoeren was doing the code generator. The three activities were intricately meshed much as co-routines with backtracking: new pseudooperations for THAT would be suggested, approved, and code restructured, requiring reorganization in some of the code already written. This procedure converged quite quickly but would not be recommended for doing an Ada compiler. in Annals of the History of Computing, 08(1) January 1986 (IBM 650 Issue) view details |