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518 THE PDP-10 FAMILY

Figure 11. DECsystem-l0 primary memory price per word versus time.

monitor of 25 percent per year, there was a positive improvement in the memory price performance. In reality, many functions for which the user was explicitly responsible were moved to the Monitor as basic operations. A similar plot for secondary memory prices is given in Figure 12.

CONCLUSI ONS

We believe the existence of the DECsystem-10 has been beneficial to the many environments for which it has provided real-time and interactive computation, including the computer science and computer engineering com

Figure 12. DECsystem-10 secondary memory price per Mwords versus time.

munities. In turn, we have tried to respond to the needs of these users. Its existence has also been a positive force in encouraging alternative, competitive products in what otherwise might have been a dull, batch environment. The system has also been used by and influenced minicomputer (and now microcomputer) development, including: hardware technology (e.g., wire-wrap), support for machine development (including simulation), and exemplary design leading to timesharing systems (e.g., DEC's TSS/8, RSTS) and user environments (e.g., RT-l 1 and microcomputer systems).

We believe the key to the 10's longevity is its basically simple, clean structure with adequately large (one Mbyte) address space. 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, therefore, the dominant system architects-implementors.

In retrospect, the machine turned out to be larger and further from a minicomputer than we had 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.

ACKNOWLEDGEMENTS

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.

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