Jane C. Blake
Managing Editor

This past spring when we surveyed Journal subscribers, several readers took the time to write comments about the particular value of the issues featuring Digital's 64-bit Alpha technology. The extraordinary engineering described in those two issues continues, with ever higher levels of performance in Alpha microprocessors, server systems, clusters, and systems software. This issue presents some recent developments: a new log-structured file system, called Spiralog; the OpenVMS operating system extended to take full advantage of 64-bit addressable virtual memory; high-performance scientific computing software for Alpha clusters connected with MEMORY CHANNEL; and speech recognition software for Alpha workstations running the Digital UNIX operating system.

Spiralog is a wholly new cluster-wide file system integrated with the new 64-bit OpenVMS version 7.0 operating system and is designed for high data availability and high performance. The first of four papers about Spiralog is written by Jim Johnson and Bill Laing who set the stage by introducing log-structured file concepts, the university research on which the designers drew, and innovations in the overall design.

The advantages of log-structured file technology over the conventional "update-in-place" file technology are explained by Chris Whitaker, Stuart Bayley, and Rod Widdowson. In their paper about the file server design, they compare the Spiralog implementation of the log-structured file technology with others and describe the novel combination of the technology with a B-tree mapping mechanism to provide the system with needed stability and data recovery guarantees.

A third paper about Spiralog, written by Russ Green, Alasdair Baird, and Chris Davies, addresses a critical customer requirement --- fast, application-consistent, on-line backup, i.e., continuous availability of data. Exploiting the features of log-structured storage, designers were able to combine the best of two backup approaches: the flexibility of file-based backup and the high performance of physically oriented backup. Consistent copies of the file system are created while applications are actively modifying data.

The Spiralog integration into the OpenVMS file system required that existing applications be able to run unchanged. Mark Howell and Julian Palmer describe the integration of write-back caching which used in Spiralog into the write-through environment used in the existing Files-11 file system. They also define the function of a write-behind cache, which allows applications to control the order of writes to the disk.

The importance of compatibility for existing 32-bit applications in a 64-bit environment is stressed again in the set of three papers about the latest step in the evolution of the OpenVMS operating system. Digital first ported the 32-bit OpenVMS operating system to the Alpha architecture in 1992. The extension of the system to exploit 64-bit virtual addressing is presented by Mike Harvey and Lenny Szubowicz. Their discussion includes the team's solution to significant scaling issues which involved a new approach to page-table residency within the OpenVMS address space.

The OpenVMS development team anticipated that applications would mix 32- and 64-bit addresses, or pointers, in the new environment. Tom Benson, Karen Noel, and Rich Peterson explain why this mixing of pointer sizes is expected and the DEC C compiler solution they developed to support the practice. In a closely related discussion, Duane Smith's paper reviews new techniques the team used to analyze and modify the C run-time library interfaces that accommodate applications using 32-bit, 64-bit, or both address sizes.

Designed for the scientific/technical user, the parallel-programming tool next described does not run on the OpenVMS Alpha system but instead on Digital UNIX Alpha clusters connected with MEMORY CHANNEL technology. Jim Lawton, John Brosnan, Morgan Doyle, Seosamh O'Riordain, and Tim Reddin present the challenges encountered in designing the TruCluster MEMORY CHANNEL Software product, which is a message-passing system intended for builders of parallel software libraries and implementers of parallel compilers. The product reduces communications latency to less than 10 microseconds in distributed shared memory systems.

Finally, Bernie Rozmovits presents the design of user interfaces for the Digital Speech Recognition Software (DSRS) product. Although the product is targeted for Digital's Alpha workstations running the UNIX operating system, the implementation issues examined and the team's efforts to ensure the product's user-friendliness can be generally applied to speech recognition product development.

Coming up in the next issue are papers on a variety of topics, including the internet protocol, collaborative software for the internet, and high-performance servers. These topics reflect areas of interest Journal readers rated near the top in last spring's survey. Our sincere thanks go to everyone who responded to that survey.