Jane C. Blake,
Managing Editor

The Digital Technical Journal marks its tenth anniversary with the publication of this issue. Since 1985, the Journal has chronicled Digital's engineering achievements from silicon to software: record-breaking microprocessors, standards-setting network technologies, advanced storage architectures, and industry-leading implementations of clusters and distributed systems. More than simply a record, the Journal offers readers insights into the how and why of Digital's product designs--in papers written by the design engineers themselves. A look back over the last ten years, however, provides only a partial view to engineering's unique combination of vision and pragmatism, a combination that has spurred industry breakthroughs and established the foundation for the development of today's world-class hardware and software products. To celebrate Digital's outstanding engineering achievements, we have therefore included a special section of historic milestones as part of this anniversary issue. The milestones begin in 1957 with the development of the company's first product, a system module for scientific use that ran at 5 MHz. The milestones continue through the recent introduction of Digital's new high-performance server system based on microprocessors that run at an extraordinary 300 MHz.

[Note: The Milestones section is not available in ASCII format.]

The 300-MHz microprocessor and the AlphaServer 8400/8200 system that uses it are in fact featured in this issue. As Dick Sites points out in his Foreword, these second-generation Alpha products truly take advantage of the Alpha 64-bit RISC architecture introduced by Digital in 1992. In addition to discussions of three Alpha hardware designs and the new microprocessor, this issue presents papers on database software technologies. These papers focus on the reality of integrating heterogeneous systems and data sources, a reality being faced by many large corporations.

The Database Integrator (DBI) directly addresses the heterogeneity issue by providing a multidatabase management system for data access and integration of distributed data sources. Richard Pledereder, Vishu Krishnamurthy, Mike Gagnon, and Mayank Vadodaria outline the data access issues and compare the DBI approach with others. Their discussion addresses such topics as heterogeneous query optimization, location transparency, global consistency, resolution of semantic differences, and security checks.

Key to solving the problems posed by heterogeneous systems are openness and standards. Both are stressed in the ACMSxp transaction processing monitor design, described by Bob Baafi, Ian Carrie, Bill Drury, and Oren Wiesler. ACMSxp is layered on the OSF's Distributed Computing Environment and uses Transarc's Encina toolkit to support XA-compliant databases. The monitor's application development environment is based on the Structured Transaction Definition Language.

The ACMSxp monitor figures in the next paper, written by Norman Depledge, Bill Turner, and Alexandra Woog, which defines an architecture for improving the effectiveness of heterogeneous environments. The authors first review relevant standards, such as CORBA and DCE, and then describe an open, distributable client-server architecture made up of three tiers: the desktop environment, middleware services (founded on the ACMSxp monitor and Digital's ObjectBroker software), and legacy application interfaces.

The next set of papers features high-performance systems built on the 300-MHz Alpha 21164 microprocessor. Presented first is the AlphaServer 8000 platform--the basis for the highest performance systems yet developed by Digital. Dave Fenwick, Denis Foley, Bill Gist, Steve VanDoren, and Dan Wissell discuss the principal design issues relative to the aggressive goals set for system data bandwidth and memory read latency. They define their design approach with seven levels of abstraction and review the choices made in each level; the prevailing theme is achieving low memory read latency. As a result, the AlphaServer 8400 and 8200 systems feature a minimum memory read latency of 260 nanoseconds (ns). Moreover, in benchmark tests, the 12-processor AlphaServer 8400 system achieves supercomputer performance levels of 5 billion floating-point operations per second.

Essential for meeting AlphaServer speed requirements was a custom application-specific integrated circuit (ASIC) bus interface. Jean Basmaji, Kay Fisher, Frank Gatulis, Herb Kolk, and Jim Rosencrans describe a timing-driven layout approach for designing and implementing high-performance ASICs. Called CSALT, i.e., CMOS standard-cell alternative technology, the tool suite saved significant project time and provided the customization necessary to support the system's 10-ns bus speed.

Developers of a second-generation processor module for the AlphaServer 2100 multiprocessing system also took advantage of the Alpha 21164 microprocessor performance and at the same time ensured physical compatibility with the first generation. Nitin Godiwala and Barry Maskas highlight the designs that most efficiently used the system bus bandwidth and provided a 1.4 SPEC performance increase over the first-generation module, including a third-level cache, duplicate tag store, and a synchronous clocking scheme.

Also based on the Alpha 21164 microprocessor, the AlphaStation 600 5-series workstation incorporates the 64-bit PCI bus and supports three operating systems. In their paper, John Zurawski, John Murray, and Paul Lemmon focus on the chips that provide high-bandwidth interconnects between the CPU, the main memory, and the PCI bus, and relate the challenges in achieving memory bandwidth goals. They also recount their experiences in the development of a hardware-based verification technique that improved test throughput by five orders of magnitude over the software-based techniques.

The Alpha 21164 microprocessor that is at the heart of the three systems described above delivers an outstanding microprocessor performance (peak) of 1.2 billion instructions per second. Three papers examine the circuit design, the logic functions, and the functional verification of this custom, 64-bit VLSI chip. First, Bill Bowhill et al. examine the circuit design contributions needed to achieve the performance goal of 300-MHz operation. The authors describe the floorplan choices for laying out the 9.3-million transistor chip and the global single-wire clock distribution scheme. They then present a set of significant circuit design challenges -- the speed requirement, the complicated microarchitecture, and the large physical size of the chip -- and explain circuit implementation decisions for the instruction, execution, and memory units; the system clock; and the three caches.

The paper by John Edmondson et al. describes the functional units of the Alpha 21164 microprocessor: the quad-issue, superscalar instruction unit; the 64-bit integer execution pipelines; two 64-bit floating-point execution pipelines; a high-performance memory unit; and a cache control and bus interface unit. The authors note architectural improvements over the first-generation 21064 microprocessor and provide performance data.

The functional verification of this complex microprocessor is described in our concluding paper. Mike Kantrowitz and Lisa Noack review the many techniques employed to verify the logic design and the PALcode interface, including implementation-directed pseudorandom exercisers used in combination with focused hand-generated tests. Also touched upon are mechanisms to check the correctness of the model representations of the microprocessor. The authors conclude by relating the lessons learned from the few bugs found in the first prototype of the microprocessor.

An anniversary is a time to look back and ahead. Looking back to the Journal's origins, I want to acknowledge the wisdom of Dick Beane, the Journal's first editor, and Sam Fuller, vice president of Corporate Research and the Journal's sponsor. They established the Journal's editorial focus and its structure: to publish technical papers, written by Digital's engineers, that describe the technological foundations of our products, under the guidance of an advisory board responsible for content and editorial philosophy. Because readers responded so well to the working engineer's perspective on product design, the Journal has grown from a biannual to a quarterly publication, and was one of the first industry journals to publish electronically on the Worldwide Web. Further, since 1992, papers have been peer reviewed to ensure that readers receive substantive, accurate information on a widening number of topics covered in the Journal. Of course this growth would not have happened without the Journal's contributors, the engineers who analyze their unique and informative experiences and share them with their peers. As Digital's engineers add to the timeline of engineering milestones in computer systems, software, networking, storage, semiconductors, and peripherals, the Journal will continue to serve its readers by publishing this important work.

The editors thank Bob Supnik, Senior Corporate Consulting Engineer, for his help in bringing together this special issue of the Journal.

Upcoming in the Journal: systems engineering, Sequoia 2000 research, software environments, scientific computing, and networking.