We believe the key to the 10's longevity is its basically simple, clean structure with adequately large (one Mbyte) address space that allows users to get work done. In this way, it has evolved easily with use and with technology. An equally significant factor in its success is a single operating system environment enabling user program sharing among all machines. The machine has thus attracted users who have built significant languages and applications in a variety of environments. These user-developers are thus the dominant system architects-implementors. In retrospect, the machine turned out to be larger and further from a minicomputer than we expected. As such it could easily have died or destroyed the tiny DEC organization that started it. We hope that this paper has provided insight into the interactions of its development. Acknowledgments. Dan Siewiorek deserves our greatest thanks for helping with a complete editing of the text. The referees and editors have been especially helpful. The important program contributions by users are too numerous for us to give by name but here are most of them: APL, Basic, BLISS, DDT, LISP, Pascal, Simula, sos, TECO, and Tenex. Likewise, there have been so many contributions to the 10's architecture and implementations within DEC and throughout the user community that we dare not give what would be a partial list. Received April 1977; revised September 1977 References 1. Bell, G., Cady, R., McFarland, H., Delagi, B., O'Laughlin, J., and Noonan, R. A new architecture for minicomputers---,the DEC PDP-11. Proc. AFIPS 1970 SJCC, Vol. 36, AFIPS Press, Montvale, N.J., pp. 657-675. 2. Bell, G., and Freeman, P. Cai-A computer architecture for AI research AFIPS Conf. Proc. Vol. 38 (Spring, 1971), 779-790. 3. Bell, G., and Newell, A. Computer Structures: Readings and Examples. McGraw-Hill, New York, 1971. 4. Bobrow, D.G., Burchfiel, J.D., Murphy, D. L., and Tomlinson, R.S. TENEX, A Paged Time Sharing System for the PDP-10. Comm. ACM 15, 3 (March 1972), 135-143. 5. Bullman, D.M. Editor, stack computers issue. Computer 10, 5 (May 1977), 14-52. 6. Clark, W.A. The Lincoln TX-2 computer. Proc. WJCC 1957, Vol. 11, pp. 143-171. 7. Lunde, A. Empirical evaluation of some features of Instruction Set Processor architecture. Comm. ACM 20, 3 (March 1977), 143- 152. 8. Mitchell, J.L., and Olsen, K.H. TX-0, a transistor computer. Proc. EJCC 1956, Vol. 10, pp. 93-100. 9. McCarthy, J. Time Sharing Computer Systems, Management and the Computer of the Future M. Greenberger, Ed., M.I.T. Press, Cambridge, Mass., 1962, pp. 221-236. 10. Murphy, D.L. Storage organization and management in TENEX. Proc. AFIPS 1972 FJCC, Vol. 41, Pt. I, AFIPS Press, Montvale, N.J., pp. 23-32. 11. Olsen, K.H. Transistor circuitry in the Lincoln TX-2. Proc. WJCC 1957, Vol. 11, pp. 167-171. 12. Roberts, L.G. Ed. Section on Resource Sharing Computer Networks. AFIPS 1970 SJCC, Vol. 36, AFIPS Press, Montvale, N.J., pp. 543-598. 13. Wulf, W., and Bell, G. C.mmp--A mutli-mini-processor. Proc. AFIPS 1972 FJCC, Vol. 41, AFIPS Press, Montvale, N.J., pp. 765-777. 14. Wulf, W., Russell, D., and Habermann, A.N. BLISS: A language for systems programming. Comm. ACM 14, 12 (Dec. 1971), 780-790. 63 Computer Systems G. Bell, S. H. Fuller, and D. Siewiorek, Editors The CRAY- 1 Computer System Richard M. Russell Cray Research, Inc. This paper describes the CRAY,1, discusses the evolution of its architecture, and gives an account of some of the problems that were overcome during its manufacture. The CRAY-1 is the only computer to have been built to date that satisfies ERDA's Class VI requirement (a computer capable of processing from 20 to 60 million floating point operations per second) [11. The CRAY-I's Fortran compiler (CVT) is designed to give the scientific user immediate access to the benefits of the CRAY-rs vector processing architecture. An optimizing compBer, cFr, "vectorizes" innermost DO loops. Compatible with the ANSI 1966 Fortran Standard and with many commonly supported Fortran extensions, CVT does not require any source program modifications or the use of additional nonstandard Fortran statements to achieve vectorization. Thus the user's investment of hundreds of man months of effort to develop Fortran programs for other contemporary computers is protected. Key Words and Phrases: architecture, computer systems CR Categories: 1.2, 6.2, 6.3 Introduction Vector processors are not yet commonplace ma- chines in the larger-scale computer market. At the time of this writing we know of only 12 non-CRAY-1 vector processor installations worldwide. Of these 12, the most powerful processor is the ILLIAC IV (1 installation), the most populous is the Texas Instru- ments Advanced Scientific Computer (7 installations) and the most publicized is Control Data's STAR 100 Copyright © 1977, Association for Computing Machinery, Inc. General permission to republish, but not for profit, all or part of this material is granted provided that ACM's copyright notice is given and that" reference is made to the publication, to its date of issue, and to the fact that reprinting privileges were granted by permission of the Association for Computing Machinery. Author's address: Cray Research Inc., Suite 213, 7850 Metro Parkway, Minneapolis, MN 55420. Communications January 1978 of Volume 21 the ACM Number 1(4 installations). In its report on the CRAY-1, Auer- bach Computer Technology Reports published a com- parison of the CRAY-1, the ASC, and the STAR 100 [2]. The CRAY-1 is shown to be a more powerful computer than any of its main competitors and is estimated to be the equivalent of five IBM 370/195s. Independent benchmark studies have shown the CRAY-1 fully capable of supporting computational rates of 138 million floating-point operations per sec- ond (MFLOPS) for sustained periods and even higher rates of 250 MrLOPS in short bursts [3, 4]. Such comparatively high performance results from the CRAY-1 internal architecture, which is designed to accommodate the computational needs of carrying out many calculations in discrete