CERN Accelerating science

Abstract

This is the first of a three-part series, made out of the original (excellent) paper written by Paolo Zanella in 1990. I hope that it can serve future Computorians to write "IT at CERN: its birth, its life ..."
- Miguel Marquina (editor)-

1. INTRODUCTION

The origins of computing machinery can be traced back to 3000 years ago when the Chinese introduced a primitive form of abacus, or 300 years ago when Schickard, Pascal and Leibniz invented the first arithmetic machines. For us at CERN it all started 30 years ago when one of the first electronic digital computers, a huge Ferranti Mercury, was installed. It was the beginning of a success story which has changed the way to do physics and, as a matter of fact, to do any work at all in the Laboratory.

The story goes on and the changes brought in by the new information technologies continue to affect us at an astonishing rate. Those who witnessed the beginning of the information era were conscious of the potential impact of those mar marvellous machines on Physics as well as on Society, but they could hardly imagine what was to come. In retrospect, we can say that the 30 years which separate us from the days of those first generation machines, have been years of struggle, of sweat and tea tears, of doubt and of painful reappraisal, but also years of discovery, of excitement, of achievement and of pride to the actors in this unique adventure.

Of those 30 CERN years, I missed only the first three. I did not miss, however, the joys of programming first generation machines, although in a different environment. Actually, when I joined CERN early in 1962, the only machines around were still made out of vacuum tubes. I am, therefore, rather well placed to tell my personal account of the what, why and how of the evolution of automatic computing at CERN.

I shall not even attempt to be exhaustive, let alone objective. I shall tell the story as I saw it, or rather as I lived it. Instead of compressing 262800 hours into 1, I shall select and report only those events which, in my opinion, are either real milestones or make an interesting story, and I shall follow them through to their consequences, even if this means breaking the strict chronological order. The basic features of the large high-performance systems which have played a major role in the CERN Computer Center are listed in Appendix 1.

2. THE BIG BANG

It took six days for God to build the Universe and a little over two years for the Ferranti engineers to produce our Mercury, a large assembly of complex circuitry hidden inside a row of austere cabinets, making few concessions ons to people's curiosity. At about the same time the PS was built in five years and today one can build accelerators 1000 times more powerful, always in about five years. The Mercury was 1000 times less powerful (16.6 kHz) than a modern personal computer which is now mass-produced by robotized assembly lines at the rate of 2 or 3 per minute!

The purchasing contract was signed on the 25th of May, 1956 and stipulated that the machine with 1024 40-bit words of fast [ 120 microsec to read/write one word from the accumulator] core store and a slow [8.75 msec latency] drum store having a total capacity of 16384 words of 40 binary digits, would be shipped to CERN in early February 1957 and installation shall be completed by 1st May, 1957.... The details of the progress of manufacture will be submitted at intervals of one month. The Mercury had a clock cycle of 60 microsec. It took 180 microsec to add and 300 microsec to multiply two long words of 40 bits. It had floating point arithmetic. Division, however, had to be programmed. It is interesting to note the absence of the word software from the contract, the only relevant mention being: any programs and sub-routines which Ferranti will prepare will be made available to CERN free of charge. Unbundling and licensing were unknown in the 50's.

The computer actually arrived during the summer of 1958 and passed the acceptance tests in October of that year. Following its successful introduction, a thick file of orders revealed the urgent need for spare valves and of tape bins (a critical device in those days of punched paper tape input/output!).

At the end of 1958, the availability of a programming language called Autocode, attracted the first users to the computer centre and marked the beginning of the 30 years of computing covered by this paper. It is interesting to note that the first Mercury Autocode compiler was written in 1956 (by R. A. Brooker), two years before the appearance of the first FORTRAN compiler! It had many features which appeared later in FORTRAN. Due to memory limitations, variable names were restricted to a single alphabetic character (5-bit Ferranti code). It is worth noting that in the mid 50's the European computer industry was still competitive. As far as competence, innovative ideas and successful products are concerned, European companies like Ferranti, English Electric and Elliott in England, Telefunken in Germany and Bull in France had little to envy their American competitors (e.g. ERA/Remington Rand, NCR, IBM). The size and the drive of the American market were, however, going to make the difference quite rapidly in the 60's.

The reasons behind the decision to acquire a Mercury were technical, political and financial. Technically the Mercury was definitely one of the most advanced machines around. It was considered superior to the Ferranti Pegasus, to the Elliott 404, to the English Electric 'Deuce', to the Bull 'Gamma 311' and to drum-type machines like the IBM 650. Ferranti was set up to produce a dozen units and CERN was going to get serial number 6. The fact that Harwell and Saclay had ordered Mercury's was given a certain weight. CERN had no experience in electronic digital computers and it was better to be part of a club of users. As to the price (one million Swiss Francs), it was five times cheaper than equivalent American machines like the ERA 1101.

Discussions went on for several months at CERN in 1955 and 1956. External experts were involved. Fifteen years after Konrad Zuse's relay-based Z3 considered by many as the first general purpose computer, ten years after the electronic ENIAC, and six years after Maurice Wilkes' EDSAC, people were still debating on the virtues of binary versus decimal machines, on the importance of floating point arithmetic, on the size of words (the Z3 had 22-bit and the EDSAC 32-bit words; the ENIAC was a decimal machine with 10 digits words. The size of central memory was 64 words for the Z3, 2n for the ENIAC and 512 for the EDSAQ, and on the best way to input and output data (punched film, 5-7-8 channels papertape, or cards). Practical problems had to do with the unreliability of the hardware, the organization of the operations and the recruitment of experts. Obsolescence was already a problem.

CERN decided that the machine should be purely binary, that 32-bit words were too short, and that the speed should be as high as possible (in particular multiplication time should be under a millisecond). It also concluded that the speed and size of memory were very important (several tens of thousands of binary digits were a clear necessity), while the availability of floating point hardware was considered a very desirable, although not quite indispensable, feature of a scientific computer. But what really makes it worthwhile to have a machine, is the enthusiasm for carrying out the most difficult computations, as an American physicist put it in a letter describing his experience with a digital computer or 'the courage to go ahead and solve problems which would have seemed too difficult to do otherwise.'

The computers of that time had colorful names like ILLIAC at the University of Illinois, AVIDAC at Argonne, MANIAC, UNIVAC, etc... Most of them were prototypes. Everything was very much experimental. The operations arrangements at the ILLIAC were described as follows: 'The user deposits his punched paper tape in a box with instructions or the operator. The operator takes these tapes, and inserts them in the machine in turn. If the code is correct, the machine delivers the answers and these may be picked up by the user the next morning. If there are errors in the code, the operator carries out the test routines requested and the results of these tests are deposited so that these may be reviewed by the user the next morning. Thus, the whole operation of the machine becomes a fairly automatic affair'. This was more or less the style adopted for our operations thirty years ago.

One of the first applications at CERN was the analysis of the papertape produced by the Instruments for the Evaluation of Photographs (IEPs), used to scan and measure bubble chamber film. The first reports convey a certain deception due to the slow tape read/write speed. Since everything had to go through the accumulator, the CPU was blocked during I/0. It was immediately clear that there was a big mismatch between the power of the computing engine and its input/output capability.

After some struggling with faulty tubes, tape bins, machine instructions and Autocode, people with lots of data discovered the existence of an IBM 704 in Paris, which offered significant advantages such as magnetic tape units, card readers, line printers and FORTRAN! FORTRAN II allowed 6-characters variable names and, most important, it simplified the exchange of programs with Berkeley and Brookhaven. The 1959 CERN Annual Report indicated already that as the needs increase, it will be necessary to envisage the replacement of the Mercury by a more powerful system. It was also quickly realized that these so-called electronic brains required quite a lot of human effort to be effectively exploited. Hence the proposal to double in 1960 the computer center staff (from 10 to 20).

So, by the end of the 50's, the fundamental forces, sociological and technological, characteristic of every computer service, had been discovered, including the illusion that upgrading the resources would solve all the problems and achieve the ultimate goal, i.e. make the users happy!

3. THE LESSONS OF THE EARLY 60'S

The next big news was the arrival of the IBM 709, an improved version of the 704, in January 1961. It was still a clumsy vacuum tube machine but it featured FORTRAN and all those fancy peripherals apt to improve the quality of life.

The word length was 36 bits, the characters became 6-bit BCD, and the core memory size jumped to 32K. The CPU was 4-5 times faster than that of the Mercury. However, to compile a typical FORTRAN program could take several minutes! Tape bins made way for card trays. Magnetic tape units read and wrote at 75 ips on 7 tracks and the density was 200 bpi. Peripherals were attached via their controllers to data channels. It was a significant advance in that it allowed as many as six peripheral devices to access core memory buffers while the CPU performed other work. Another important device which came with the 709 was the so-called Direct Data Connection, allowing for direct transmission of data from external equipment to memory via a channel. The speed was not ridiculous: in principle up to 1 Megabit/sec. The 709 was also equipped with one of the first interrupt systems.

The bad news was still the poor reliability, although the progress was already quite substantial. Unscheduled maintenance represented 11% of the total time. Scheduled maintenance took away a time slice of similar size. So the down-time of the 709 compared not too unfavorably with the up time of the very first electronic computers.... The on-line card reader and the printer did, however, slow down the operations considerably. After one year of experience CERN added a small IBM 1401, in order to speed up the input/output, the job sequencing and the operations. The concept of SPOOLing (Simultaneous Peripheral Operation On-Line) with its 1/0 files (virtual reader/printer) has its origins in those days. Programming for the 709 was considered a difficult activity to be left to the specialists who could understand and keep up-to-date with the new techniques and the operating conventions. The machine was an expensive resource which had to be used efficiently. To give an idea, the list price was in the region of ten millions francs (1960 Swiss francs!). In those days a magnetic tape cost 60 $ (some 260 SF!). It was at that time that the first inescapable committees appeared, e.g. Computer Scheduling Committee, Computer Users Advisory Committee and the Data Handling Policy Group.

The Mercury had still its faithful users but suffered from the chronic lack of modern, fast peripherals. In 1962, as part of a lifting operation, it was enhanced by the connection of an Ampex tape unit, compatible with IBM specifications and operating at 3333 characters per second (over 3 times the speed of the fastest paper tape reader and some 20 times faster than a tape punch). Also, two papertape-to-card converters were installed to ease the transfer of data from the Mercury to the 709. By the end of 1962 it was possible to read the paper tape from IEPs into the Mercury, give it a first processing pass, write the results on magnetic tape and input it onto the IBM 709 for further analysis. The first application packages appeared at that time, e.g. THRESH and GRIND used for the geometrical reconstruction and kinematic analysis of bubble chamber events. It is amusing to note that, in spite of the growing workload and the frantic development of codes, the machines were normally switched off at weekends. But the practice of 24 hours/day, 7-days/week service was around the corner. It is also in interesting to realize that things like the connection of the Ampex tape unit to the Mercury were entirely designed and implemented on site.

The next problem was how to use all those Autocode programs on the 709. One just wrote an Autocode compiler for the 709. The difficulties of developing software were soon to be learned. The first Conference recognizing the existence of a software crisis was held in Munich in 1968. Why is software always late and unreliable? People working today with modern CASE (Computer Assisted Software Engineering) or OOP (Object Oriented Programming) tools are still trying to solve the problem. But the answer in those days was: better programming languages.

CERN FORTRAN was defined to ensure compatibility with other laboratories and facilitate portability of codes. It was felt, however, that FORTRAN was used mainly for historical reasons and new, more powerful languages would be needed to fully exploit the potential of the electronic computer. As we all know, CERN was not affected by, or it missed completely, the language explosion which started in the early 60's. ALGOL, Lisp, PL/I, PASCAL, Modula II, ADA, C, PROLOG, etc... did not raise above the level of minority cultures. FORTRAN evolved through its versions II, IV, 66, 77, 8X, and it still dominates the CERN programming landscape.

It took some time to saturate the 709, but it was already clear that young physicists were becoming addicted. It was at that time that the first embryonic Operating System appeared under the name of FORTRAN Monitor System. Many other important events occurred in the early 60's, such as the connection of computers on-line to film measuring devices including the very fast automatic flying spot digitizers (HPD, Luciole, etc..) forerunners of the modern image digitizers and the first attempts to connect computers directly to experimental equipment (on-line experiments). The IBM 709 was operated on-line to an HPD to measure both bubble and spark chamber films. In September 1963 the 709 was replaced by a 7090, a transistorized version of the same machine, about four times more powerful.

It was at that time that the investments and the efforts started to pay off. Over 300 000 frames of spark chamber film were automatically scanned and measured in record time using an HPD Flying Spot Digitizer on-line to the 7090. At about the same time computers were connected on-line to experiments to monitor the equipment and to collect digital data from the first filmless detectors (e.g. sonic spark chambers) onto magnetic tape. The first successful demonstrations with fully auto automatic digital pattern recognition showed that computers could be programmed to replace slow human operators in a variety of tasks. Stories about computers doing things faster, better and more reliably than human beings got around producing the usual mixture re of emotional reactions. In 1970 the European Physics Society held a Conference at CERN on the 'Impact of Computers on Physics' and I remember the reassuring statement of an eminent physicist that 'so far computers have not significantly contributed to any discovery'. It was going to take another decade to see the HEP community wholeheartedly accepting the computer as a critical component of their research and admitting it to their current technological foundation trilogy: accelerators, detectors and computers.

1970 was also the year when the 'CERN Computing and Data Handling School' was launched to educate young physicists and stimulate the sharing of computing experience between high-energy physicists and computer scientists. It turned out to be an excellent idea. The School is still alive and well, fulfilling a clear need. As to the cross-fertilization across the physics/computer science boundary, it has developed into an ideal partnership.

Actually the two disciplines have influenced each other from the very beginning. It was the physicist Bruno Rossi who built the first logic circuits which then were developed into computer hardware, and physicists have always been among the most demanding consumers of computer cycles. Enrico Fermi, when asked in the early fifties which research project would he recommend to the young Italian physicists, told them to design and build a computer. Indeed, physics research could not have become what it is without the computer, and conversely, the development of the computer has been deeply influenced by the needs and vision of basic research.

The study of the fundamental properties of elementary matter involves the frontiers of human knowledge and pushes the technology to the limit of what is possible. Computer scientists have been playing with models and formalisms, architectures and languages, inventing tools and methodologies of a rather theoretical nature and they have been sometimes accused of developing general solutions in search of specific problems. When a dense problem space meets a rich solution space some good news can be expected... Evidence of synergistic effects has been accumulating ever since the beginning of the information era. High-energy physics and information technology are among those disciplines which, in the second half of our century, have shown the most impressive advances.

All the major computers having served in the CERN Computer Centre in the period 1958-1988 are listed in chronological order, together with some configuration details and their characteristic features.

FERRANTI 'Mercury' [1958-1965]

First generation vacuum tube machine (60 microsec clock cycle, 2 cycles to load or store, 3 cycles to add and 5 cycles to multiply 40 bit longwords, no hardware division) with magnetic core storage (1024 40-bit words, 120 microsec access time). Mercury's processor had floating point arithmetic and a B-Register (index register). Magnetic drum auxiliary storage (16 Kwords of 40 bits, 8.75 msec average latency, 64 longwords transferred per revolution). Paper tape I/0. Two Ampex magtape units added in 1962. Autocode compiler. At the end of its career it was connected on-line to an experiment (Missing Mass Spectrometer). In 1966 the Mercury was shipped to Poland as a gift to the Academy of Mining and Metallurgy at Cracow.

IBM 709 [1961-1963]

Vacuum tube machine (12 microsec clock cycle, 2 cycles to add and 15 on average to multiply 36 bit integers, hardwired division and floating point arithmetic, index registers) with core storage (32 Kwords of 36 bits, 24 microsec access time). Card reader (250 cpm) and card punch (100 cpm). Line printer. Magtape units (7 tracks, 75 ips, 200 bpi). Introduction of the Data Channel. FORTRAN compiler. FORTRAN Monitor System.

IBM 7090 [1963-1965]

Transistorized second-generation machine ( 2.18 microsec clock cycle) with core storage (32 Kwords of 36 bits, 4.36 microsec access time). Card 1/0, Tape units (7 tracks, 112.5 ips, 200/556 bpi). Eight Data Channels. Interrupt System. FORTRAN compiler. Basic Monitor Operating System (IBSYS). Connected on-line to Flying Spot Digitizers (HPD and Luciole) to measure bubble and spark chamber films.

CDC 6600 [1965-1975]

Serial Number 3 (pre-production series machine). Transistor machine designed by Seymour Cray and very compact for its time. CPU clock cycle 100 nsec. Core memory: 128 Kwords of 60 bits. Memory access 1 microsec, but independent memory banks allowed for up to one access per clock cycle. Instruction prefetch. Ten overlapping functional units. Ten autonomous peripheral processor units (PPU's) each with 4K of 12-bit words core memory. Huge disks over one meter in diameter holding 500 million bits. Tape Units (half inch tape, 7 tracks, 200, 556 and 800 bpi, and one inch tape, 14 tracks, 800 bpi). High-speed card reader (1200 cpm).

First multi-programmed machine in the Computer Centre. However, SIPROS multiprogramming operating system was abandoned by Control Data. Basic SIPROS operating system had to be made at CERN. Then Chippewa OS (COS) was installed. It evolved to SCOPE which was eventually used after adapting it to CERN needs. This resulted in a non-trivial amount of changes, thus deserving the renaming to CERN SCOPE. The 6600 was connected to various FSD systems and to two on-line computers, the SDS920 and the IBM 1800, via CERN-made data links. In terms of processing capacity the 6600 was about three quarters of a CERN unit or ten times the 7090.

The change-over from the IBM 7090 was planned to take three months starting in January 1965. Major engineering overhauls had to be done instead during the first few years and ended up in a two-months shut-down in 1968 in order to modify the 6600 to incorporate logic and packaging improvements which had been introduced in the production machines. During this long period of struggling with hardware instabilities and software development and changes, computing work was done partly by sending jobs to outside computers and partly by processing data on a CDC 3400, and later on a 3800, temporarily made available at CERN by Control Data.

CDC 3800 [1966-1968]

The 3800 was a member of the 3000 series CDC family of computers, incompatible with the 6000 series machines. More conventional than the 6600, the 3800 had a 48-bit architecture. The core memory (64 Kwords) was replaced by a faster one (800 nsec) during its staying at CERN. This machine was eventually acquired by the State of Geneva and installed at the local University. At CERN it was replaced by a CDC 6400. It is worth noting that CERN acquired other machines of the 3000 s series, e.g. a 3100 for the FOCUS project offering semi-interactive facilities and quick sampling of experimental data at the central computers, and a 3200 for interactive graphics applications.