Computers of the Next Generation Stretch -100 times faster than the IBM 704
STRETCH
is the name given to an advanced machine development project of the IBM Corp., which is the result of a contract between the U. S. Atomic Energy Commission and IBM. This paper indicates some of the problems encountered in developing the organization of the Stretch computer. The speed at which modern storedprogram digital computers will run is limited by the speed of the storage device used. Most intermediate and low-speed computers use magnetic drum storage and most high-speed computers use magnetic core storage. The fastest magnetic core storage available a t the time of signing the contract was only twice that of the Type 704. However, new core materials gave promise of a 2-microsecond cycle time and new winding techniques with multipath cores gave promise of 0.5-microsecond cycle times in small arrays. T o back up these increased memory speeds, a very fast arithmetic unit had to be developed. One of the limiting factors in building an ultra-high-speed computer is physical size. As the speed limit of a particular component is approached, many more components are required to perform a given logical task. The 4000 square feet required for a 704 installation had expanded to over 20.000 feet for a single Sage computer, only doubling or tripling speed. Clearly, a new device was needed. Bench testing of a new type of transistor had indicated speed potential in the IO-megapulse range. I t was felt that a n arithmetic unit could be constructed, using the new transistor, to give floating point addition in about 0.6 microsecond and floating point multiplication in about 1.2 microseconds. Transistors had the additional appeal of lower heat dissipation and much higher reliability than vacuum tubes. Speed Objectives. The speed goal is 100 times the performance of the Type 704. The main bulk of storage, however, will have a speed of 2 microsecondsonly six times that of the 704. The highspeed storage, necessarily available in smaller arrays, has a speed of 0.5 microsecond-only 24 times that of the 704. Obviously, the Stretch computer could not be organized in the same way as the Type 704. Examination of the operation of the 704 shows that in some operations, like fixed point addition, the memory is busy full time-two memory cycles being required. I n operations like floating point addition, multiplication, and division, the
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memory is busy only 10 to 25% of the time. A machine which could take advantage of these idle times could run faster. To accomplish this, Stretch has been organized so that portions of the machine operate independently of each other. The main computer delegates such things as indexing and input-output control to other parts of the machine organization, each of which runs independently until it requires information from another section. Instead of one storage array, several independent storages, each with its own register complement, feed into a common memory buss. The heart of this organization is a built-in “scheduler,” which is constantly aware of the progress of the program and the status of each unit. Its function is to “optimum progqam” the operation and interaction of ad sections for maximum efficiency. I n the evaluation of possible design configurations, it was necessary to test Stretch on actual problems. As expected, the speed advantage of Stretch over the 704 is heavily dependent on the sequence of operations required. The timing of programs was an extremely onerous task, because all parts of the machine had to be evaluated at 0.1-microsecond intervals throughout an entire problem. T o aid in this study, a simulation program has been written for the 704 which will accept a Stretch program and analyze it for speed. The 704 program also gathers statistics on such things as the percentage activity in various parts of the machine and the number of times each part had to wait on another part. In this way, it has been possible to evaluate the effect, for example, of increasing the number of independent memory units us. increasing the speed of each unit. Machine characteristics are as follows : The word size is 64 binary bits, plus eight check bits. Instructions are single addresses with provision for variable field length arithmetic in both the binary and decimal modes. A full complement of single and double precision floating point commands is provided. A floating point word consists of a 48-bit mantissa plus sign and an 11-bit exponent plus sign. There are 16 index registers. Particular attention is being paid to reliability and serviceability. An errorcorrecting code will automatically correct all single errors during data transmission. Error-recording devices will keep track of the number of error corrections made by the machine, and indicate the area of the fault. Machine features which contribute to programming ease will also be provided. An automatic interrupt feature allows the
INDUSTRIAL AND ENGINEERING CHEMISTRY
program to take action on any or all of 64 machine conditions. An address limit may also be set to give an alarm in case the program tries to address memory outside of a designated area. Working along with the Stretch development is a project for development of a programming system. Close cooperation is maintained between these two groups to ensure that machine features are included in the design which will assist in automatic programming. Findings to date indicate that the goal of achieving 100 times the 704 speed is achievable. The development program is still on schedule and it is planned to deliver the first machine to Los Alamos in 1960.
L. C. HUBBARD lnternational Business Machines Corp., 3625 West 6th St., Los Angeles 5, Calif. RECEIVED for review April 25, 1958 ACCEPTEDJuly 29, 1958
Analogs-reaching every field
into
C o m m I s o N of present activity levels reveals a certain domination of the computer field by digital equipment. However, the modern electronic analog computer has been in existence for less than two decades and it is unlikely that it adequately represents the total analog class and its potentialities. To achieve a true perspective for any investigation of the future of analog computation, knowledge of the history of analog computers and the present state of the art is necessary. Man’s application of the method of analogy has taken diverse forms. From direct models there has been progression through indirect models of increasing flexibility and utility, culminating in an instrument currently identified as the electronic analog computer. I t is generally accepted that electronic analog computers represent the best expression of analog techniques yet attained. The electronic analog computer is an aggregate of high gain direct-coupled operational amplifiers with associated passive impedances, and other elements such as potentiometers, diodes, multipliers, and function generators that can be programmed by interconnection to generate problem solutions for presentation on readout equipment. Soon after the direct current operational amplifier was introduced as the basic analog computer element, a number of refinements
greatly extended its scope. Notable were amplifier stabilization, prepatch panels, and precision nonlinear components. For several years computers possessed computational capabilities beyond the requirements of problems then under consideration. Developments during this period were primarily the outgrowth of an introspective appraisal by the computer industry rather than healthy conceptual advances in response to problem demands. An examination of present and contemplated analog computer applications, with a knowledge of available equipment, should provide a basis from which to extrapolate future analog developments. Present-day usage can be broadly categorized into three areas of application : general-purpose computation, simulation, and instrumentation. The great majority of analog computing equipment is of the general-purpose computation type. Commercial analog computers are specifically designed for this use, and can conveniently handle a great variety of problems. In normal operation the operator first prepares a computer diagram from the mathematical expression of a problem. Constants of proportionality, called scale factors, are established to relate physical variables to the operating range of varying direct current voltages in the computer. The computer is proqrammed by manually interconnecting its elements in accordance with the computer diagram and entering parameter values and initial conditions as potentiometer settings. When the computer is activated, computation proceeds at an arbitrarily chosen time rate, and the results are generated as functions of voltage us. time. Interpretation of results by the operator yields the solution. Analog computers play significant roles in simulation and instrumentation activities. Simulation might be described as a compromise of reality and analogy. A portion of a device or system is physically realized; the remainder is represented analogously. Because of its great powers of mimicry, the electronic analog computer is finding increasing employment in simulation work. With appropriate input and output transducers, analog computer elements can operate successfully in conjunction with virtually any other type of equipment-even digital computers. Computers operating as simulators must perform fixed functions in real time and generally do not require the programming and time scale flexibility of the general-purpose machines. The third major use category is in instrumentation. Linearization and computation can be readily performed by an assemblage of analog components, and the great flexibility afforded by computer elements makes them well adapted
for controller applications. Computer use in instrumentation is relatively new, but probably this will be the dominant area of computer application. Electronic analog computefs are probably best suited to the simulation field by their very nature and capability, and the requirements of simulation situations. Available three- or four-place analog computer accuracy is adequate for most simulation tasks, because of the degree of tolerance found in physical systems and the accuracy of existing transducers. I t is doubtful that simulation considerations will greatly influence future computer design and development. Instrumentation requirements, however, will probably exert a strong force, particularly in component development; the narrow life zone of existing electronic analog equipment is often inadequate for the severe conditions imposed by instrumentation use, and component reliability is questionable for incorporation as an integral part of a costly system or process. Highly specialized computing elements with exceptional reliability, operable in rigorous environmental circumstances, will soon emerge. Magnetics and solid state devices will be used to fortify analog computers for instrumentation service. Computing elements will be individually powered and programming may be accomplished without the expensive control units of the generalpurpose computer. Changes in logic will enhance employnient in instrumentation and process work. Analog cbmputers programmed to check and diagnose their own circuitry and select alternative equipment in the event of failure could be assembled now, and will appear if required. Present instrumentation applications are merely pilot installations that point the way to total utilization when instrument men understand the analog art, and more appropriate equipment becomes available. The most significant and revolutionary changes in analog computers will occur in response to ever-increasing demands in general-purpose applicability. Initially the changes will be in the form of appendages to a standard operational amplifier electronic analog computer; certain of these are already in evidence. Servo-set potentiometers, tape proooramming, digital print-out, and punch card function generator setup are recent computer developments specifically designed for the general-purpose user. There will be automatic balancing of all computing elements, amplifiers, multipliers, function generators, etc., arbitrary function generators with semi- or fully automatic setup and a function memory for rapid re-entry, and automatic programming of standard computational forms. Some of these features will be available in a few years. High-speed digital units will appear as internal elements in analog computers, to supply accurate non-
linear and later linear operations. With an internally digitized analog computer, completely automatic programming can be realized and many operator functions will be incorporated into the machine. The interconnection of computer elements now accomplished by manual patching will be fully automatized and even scaling and problem schematic preparation may become machine functions. These design changes will permit the use of advanced techniques new to the analog field. Iteration, multiple timescale operation, and parameter optimization will be mechanized and available as automatic computational procedures. In specialized applications, such as control system design, the computer of tomorrow may formulate the problem statement by direct interrogation of the plant through transducers and strategically located sensors. The computer will program itself to solve the problem, and by iterative techniques and parameter variance will present as the solution the optimum controller configuration and settings. The sophisticated and complex computers of the future will have little resemblance to previous analogs, in functional operation or computational procedure, b,ut they will still solve problems by analogous representation, ahd must therefore be identified as analog computers. Computer design changes and new and extended problem-solving methods generally result from existing needs, but each advance opens fields of computer applicability, which present new challenges and unsolved problems. The digitized analog with its automatic programming and associated techniques will everitually prove inadequate for the exploding universe of computer utilization. Totally new computational methods will evolve, analogous to human thought processes, and computers with undreamed of speed, accuracy, and data handling capabilities will result. The new analogs will supply decisions based upon factual analysis to replace human estimates and opinions in many problem areas considered beyond the scope of machine performance ability. These computers will accept information from a complex of input sources, and evaluate and implement computed results. The analog computer of today has achieved a prominent status in industrial and scientific activity, but the influence of analog computers of the future will reach every field of human endeavor.
DAVID R. MILLER Computer Systems Laboratory, Colorado Resfarch Corp., Denver, Colo. RECEIVED for review April 25, 1958 ACCEPTED July 29, 1958 VOL. 50, YO. 1 1
NOVEMBER 1958
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