Jane C. Blake,
Managing Editor

The integration of personal computers in a network environment is the subject of this issue of the Digital Technical Journal. The software products that bring about this integration are known collectively as PATHWORKS and are derived from Digital's Personal Computing Systems Architecture. The engineering challenge for developers was to integrate a variety of client (PC) and server systems-DOS, Windows, OS/2, Macintosh, VMS, and ULTRIX-and to ensure that the intricacies of the meshing of these systems remained transparent to PC users.

In the opening paper, Alan Abrahams and David Low provide background for the papers that follow by describing the technical aspects of the various hardware and software platforms, physical networks, and protocols that had to be addressed by PATHWORKS developers. They also present an overview of the PATHWORKS components which allow PC users to access network resources, including files, printers, databases, and mail systems.

Among the capabilities PATHWORKS enables, PC access to files on server systems is one of the most important for users. Two file servers, one for VMS and another for ULTRIX, were developed for this purpose. A paper on the development of the first of these, written by Ed Bresnahan and Siu Yin Cheng, contains an architectural overview of the VMS file server. The authors also detail the mapping done to bridge the differences between DOS, OS/2, and VMS operating systems, including the interesting problem of mapping DOS files organized as byte streams and VMS files organized as collections of records. In a related paper, Phil Wells describes performance improvements made in version 4.0 of the file server which were achieved by optimizing the transport interface and the data buffering algorithm. He discusses the analysis of server performance for various interface models, the implementation of the algorithm in the VMS server, and benchmark test results.

Like the VMS file server, the PATHWORKS software for ULTRIX systems integrates PC clients with a server system on a LAN. However, as Anthony Rizzolo, Beth Brewer, and Martha Chandler explain in their paper, a multiple process model was chosen rather than the single process used in the VMS file server. The authors give their reasons for this different approach as part of a general discussion of the server design and implementation.

The network is key to the exchange of data in the PATHWORKS environment, and as is the case for the server software, multivendor systems must be addressed to ensure smooth integration. Mitch Lichtenberg and Jeff Curless describe how Digital has extended Microsoft's LAN Manager across a LAN or a WAN by using the DECnet transport protocol as the transport layer in PATHWORKS products. In addition to presenting the reasoning behind the design of the transport component for DOS and OS/2 products, they review steps taken to reduce memory usage, improve performance, and reduce maintenance costs.

Further details on the integration of DECnet and LAN environments are provided in the paper on two network virtual device drivers for the Microsoft Windows environment. As Andy Nourse explains, these drivers manage DECnet and NetBIOS operations and enable the Windows operating system to support peripheral devices, memory resources, and software applications. Andy first gives readers background on the Windows operating modes, emphasizing the enhanced mode in which the drivers are available. He then describes the development and capabilities of the two virtual device drivers.

A significant new application in the PATHWORKS family, called eXcursion, brings together the capabilities of X Windows, DECnet, and the Microsoft environment, resulting in the display of both Windows and X Windows on the same screen. Dennis Giokas and Andy Leskowitz present the integration philosophy behind the display server and the implementation of the server architecture. They also relate how designers approached the mapping of the windows, graphics context, fonts, and color maps in the X and Windows environments.

The issue concludes with a paper by Chris Methot on capacity modeling of PATHWORKS client-server workloads. Chris describes a queuing analytical model used to understand resource consumption on the server and the special modeling process required in the client-server environment. The paper works through a specific example of the model's identification of bottlenecks in the system.

The editors thank Star Dargin and Carnel Hoover of the Personal Computing Systems Group for their help in preparing this issue.