Jane C. Blake,
Managing Editor

This issue's opening section features audio and video technologies that exploit the power of Digital's 64-bit RISC Alpha systems. Papers describe new software and hardware designs that make practical such applications as text-to-speech conversion and full-motion video on the desktop. A second set of papers shifts the focus to the UNIX environment with discussions of high-availability services and of Encore Computer Corporation's new real-time debugging tool.

The opening paper for the audio and video section references an audio technology that physicist Stephen Hawking uses to convert the text he types to highly intelligible synthetic speech. Recently, engineers have ported this mature 10-year-old hardware technology, called DECtalk, to text-to-speech software. Bill Hallahan explains that the computational power of Digital's Alpha systems now makes it possible for a software speech synthesizer to simultaneously convert many text streams to speech without overloading a workstation. After reviewing relevant speech terminology and popular synthesis techniques, he describes DECtalk Software multithreaded processing and the new text-to-speech application programming interface for UNIX and NT workstations.

Video technologies -- full-motion video on workstations -- also capitalize on the high performance of Alpha systems. In the first of four papers focused on digital video, Ken Correll and Bob Ulichney present the J300 video and audio adapter architecture. To improve on past full-motion video implementations, designers sought to allow video data to be treated the same as any other data type in a workstation. The authors review the J300 features, including a versatile color-map rendering system, and the subsystem design decisions made to keep product costs low.

Victor Bahl then presents the J300 software that controls the hardware. The challenge for software designers was to obtain real-time performance from a non-real-time operating system. A description of the video subsystem highlights the video library and an innovative use of queues in achieving good performance. This software architecture has been implemented on OpenVMS, Window NT, and Digital UNIX platforms.

A third paper on video technology looks at delivering video without specialized hardware, that is, a software-only architecture for general-purpose computers that provides access to video codecs and renderers through a flexible application programming interface. Again, faster processors make a software-only solution possible at low cost. Authors Victor Bahl, Paul Gauthier, and Bob Ulichney preface the paper with an overview of industry-standard codecs and compression schemes. They then discuss the creation of the software video library, its architecture, and its implementation of video rendering that parallels the J300 hardware implementation.

The final paper in the audio and video technologies section explicitly raises the question of what features are best implemented in hardware and what in software. The context for the question is a graphics accelerator chip design that integrates traditional synthetic graphics features and video image display features -- until now, implemented separately. Larry Seiler and Bob Ulichney describe the video processing implemented differently in two chips, both of which offer significantly higher performance with minimal additional logic.

The common theme of our second section is the UNIX operating system. Larry Cohen and John Williams present the DECsafe Available Server Environment (ASE), which provides high availability for applications running on Digital UNIX systems. They describe the ASE design for detection and dynamic reconfiguration around host, storage device, and network failures, and review key design trade-offs that favored software reliability and data integrity.

Mike Palmer and Jeff Russo then contrast Encore Computer Corporation's set of debug and analysis tools for real-time applications, called Parasight, with conventional UNIX tools. They examine the features that are critical in an effective real-time debugging tool, for example, the ability to attach to a running program and to analyze several programs simultaneously. A description follows of the Parasight product, which includes the features necessary for real-time debug and analysis in a set of graphical user interface tools.

Upcoming in our next issue are papers on a variety of topics, including Digital UNIX clusters, eXcursion for NT, and network services.