The X Window System, Version 11, is the standard window system on Linux and UNIX systems. X11, designed in 1987, was “state of the art ” at that time. From its inception, X has been a network transparent window system in which X client applications can run on any machine in a network using an X server running on any display. While there have been some significant extensions to X over its history (e.g. OpenGL support), X’s design lay fallow over much of the 1990’s. With the increasing interest in open source systems, it was no longer sufficient for modern applications and a significant overhaul is now well underway. This paper describes revisions to the architecture of the window system used in a growing fraction of desktops and embedded systems 1

In a new version of the Unix operating system, a flexible coroutine-based design replaces the traditional rigid connection between processes and terminals or networks. Processing modules may be inserted dynamically into the stream that connects a user's program to a device. Programs may also connect directly to programs, providing interprocess communication. Introduction The part of the Unix operating system that deals with terminals and other character devices has always been complicated. In recent versions of the system it has become even more so, for two reasons. 1) Network connections require protocols more ornate than are easily accommodated in the existing structure. A notion of "line disciplines" was only partially successful, mostly because in the traditional system only one line discipline can be active at a time. 2) The fundamental data structure of the traditional character I/O system, a queue of individual characters (the "clist"), is costly because it accepts and dispense...

Graphical user interfaces are difficult to implement because of the essential concurrency among multiple interaction devices, such as mice, buttons, and keyboards. Squeak is a user interface implementation language that exploits this concurrency rather than hiding it, helping the programmer to express interactions using multiple devices. We present the motivation, design and semantics of squeak . The language is based on concurrent programming constructs but can be compiled into a conventional sequential language; our implementation generates C code. We discuss how squeak programs can be integrated into a graphics system written in a conventional language to implement large but regular user interfaces, and close with a description of the formal semantics. CR Categories: I3.6 Graphics languages, Interaction techniques D3.1 Formal semantics CR General Terms: Algorithms, Theory, Languages Additional Keywords: Concurrency, User Interfaces Introduction User interface implementation languag...

The Blit is an experimental bitmap graphics terminal built for research into interactive computer graphics on the UNIX time-sharing system. The hardware is inexpensive and the graphics functions are implemented entirely in software. Nevertheless, the graphics performance of the Blit is comparable or superior to some displays with special purpose graphics hardware. This paper explains the paradox by referring to some principles of design: the hardware and software should be designed together to complement each other; carefully designed software can outperform infelicitous hardware; and simplicity of design leads to efficiency of execution. These principles are illustrated by examples from the Blit hardware and software and comparisons with other systems. March 30, 2000 _______________ * Current address: Bell Laboratories Murray Hill, New Jersey 07974 AT&T Bell Laboratories Holmdel, NJ 07733. Current address: Valid Logic Systems, Mountain View CA 94043 Hardware/Software Trad...

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When implemented in a concurrent language, a window system can be concise. If its client programs connect to the window system using an interface defined in terms of communication on synchronous channels, much of the complexity of traditional eventbased interfaces can be avoided. Once that interface is specified, complex interactive programs can be assembled, not monolithically, but rather by connecting, using the same techniques, small self-contained components that each implement or modify elements of the interface. In particular, the window system itself may be run recursively to implement subwindows for multiplexed applications such as multi-file text editors. This is the software tool approach applied to windows.

Programming environments support revision control in several guises. Explicitly, revision control software manages the trees of revisions that grow as software is modified. Implicitly, editors retain past versions by automatically saving backup copies and by allowing users to undo commands. This paper describes an editor that offers a uniform solution to these problems by never destroying the old version of the file being edited. It represents files using a generalization of AVL trees called “AVL dags, ” which makes it affordable to automatically retain past versions of files. Automatic retention makes revision maintenance transparent to users. The editor also uses the same command language to edit both text and revision trees.

Sam is an interactive multi-file text editor intended for bitmap displays. A textual command language supplements the mouse-driven, cut-and-paste interface to make complex or repetitive editing tasks easy to specify. The language is characterized by the composition of regular expressions to describe the structure of the text being modified. The treatment of files as a database, with changes logged as atomic transactions, guides the implementation and makes a general ‘undo’ mechanism straightforward. Sam is implemented as two processes connected by a low-bandwidth stream, one process handling the display and the other the editing algorithms. Therefore it can run with the display process in a bitmap terminal and the editor on a local host, with both processes on a bitmap-equipped host, or with the display process in the terminal and the editor in a remote host. By suppressing the display process, it can even run without a bitmap terminal.

The Plan 9 window system, 8 1 /2 , is a modest-sized program of novel design. It provides ASCII I/O and bitmap graphic services to both local and remote client programs by offering a multiplexed file service to those clients. It serves traditional UNIX files like /dev/tty as well as more unusual ones that provide access to the mouse and the raw screen. Bitmap graphics operations are provided by serving a file called /dev/bitblt that interprets client messages to perform raster operations. The file service that 8 1 /2 offers its clients is identical to that it uses for its own implementation, so it is fundamentally no more than a multiplexer. This architecture has some rewarding symmetries and can be implemented compactly

The original UNIXÒ system was designed to be small and intelligible, achieving power by generality rather than by a profusion of features. In this spirit we have designed and implemented IX, a multilevel-secure variant of the Bell Labs research system. IX aims at sound, practical security, suitable for private- and public-sector uses other than critical national-security applications. The major security features are: private paths for safe cooperation among privileged processes, structured management of privilege, and security labels to classify information for purposes of privacy and integrity. The labels of files and processes are checked at every system call that involves data flow and are adjusted dynamically to assure that labels on outputs reflect labels on inputs. 1. INTRODUCTION We have built IX, an experimental "multilevel secure" variant of the UNIX operating system. IX supports document classification with mandatory access control; classified input must yield classified out...