Jane C. Blake,
Managing Editor

Digital recently announced record-breaking 30,390 tpmC performance on a Digital UNIX cluster of 64-bit RISC AlphaServer systems. In this issue, engineers from the UNIX team describe the key technologies that enable these near supercomputer performance levels as well as provide the cluster characteristics of high availability and scalability. Also presented in this issue are advanced UNIX programming tools for maximizing performance, X server software that supports the Microsoft family of operating systems, and new network directory services that simplify management.

First defined by Digital in the early 1980s, clusters are highly available, scalable multicomputer systems built with standard parts and offering the advantages of single-computer systems. Wayne Cardoza, Fred Glover, and Sandy Snaman compare clusters with other types of multicomputer configurations and describe the major components of Digital's newest cluster implementation, TruCluster systems, for the 64-bit UNIX environment. The cluster interconnect, called MEMORY CHANNEL, is critical to the cluster's outstanding performance. MEMORY CHANNEL implements clusterwide virtual shared memory and reduces overhead and latency by two to three orders of magnitude over conventional interconnects.

Also developed for the Digital UNIX environment (version 4.0) are two program analysis and optimization tools -- OM and Atom. The tool technology originated in Digital's Western Research Laboratory, where researchers focused on providing performance diagnosis and improvements for large customer applications. Software developers Linda Wilson, Craig Neth, and Mike Rickabaugh from the UNIX Development Environment group describe the object modification tools and the flexibility they provide over traditional tools that are implemented in the realm of compilers. In addition to demonstrating practical application of the tools, the authors examine the process of transferring technology from research to development.

For mixed operating system environments, Digital developed Windows-based X server software, called eXcursion, to allow the windows of a remote host running UNIX or OpenVMS to display on a desktop running the Microsoft Windows operating system. The latest version of eXcursion, described here by John Freitas, Jim Peterson, Scot Aurenz, Chuck Guldenschuh, and Paul Ranauro, is wholly rewritten to maximize graphics performance and to support the full range of Windows platforms: Windows, Windows 95, and Windows NT. This new version is based on the X Window System version 11, release 6 protocol from the X Consortium.

Two network directory services that reduce complexity and increase choices for network managers are the subjects of our next papers. The first is designed for multiple networked environments; Integrated Directory Services (IDS) software integrates multiple services into one directory-service-independent system. Margaret Olson, Laura Holly, and Colin Strutt outline the problems that have limited the use of directory services and the different design approaches the team considered to simplify directory services use and make it more attractive. They then describe the IDS extensible, object-based framework, which comprises an application programming interface and a service provider interface. Next, Rich Rosenbaum and Stan Goldfarb present the Common Directory Interface (CDI) for DECnet/OSI. Implemented as shared libraries in the Digital UNIX and OpenVMS operating systems, CDI is designed to give network managers a choice of directory services. The authors describe the libraries and the registration tool set of management operations that is layered on a specialized API.

Coming up in the Journal are papers about a new log-structured clusterwide file system called Spiralog, the 64-bit OpenVMS operating system, speech recognition software, and the UNIX clusters message-passing system and its use for program parallelization.