Is X Window System Available on any Machine NOT Running UNIX?
The majority of X implementations are for UNIX systems. However, there are other (compatible) implementations that run on VMS, Apollo DOMAIN, and others. When using a true multitasking operating system, an X client (like an engineering design application) can be run on the same CPU as the X display server. In fact, this is the usual pattern for using X: display server and multiple clients running on the same (multitasking) CPU.
Does Compatibility Mean the Macintosh OS Being Able Run to Window X?
You can also run an X display server on a single-user operating system, such as the Macintosh OS or MS-DOS. These implementations require all the X client applications to be run remotely. Some terminal manufacturers (Wyse is one example) have produced intelligent terminals that operate as X display servers. (These terminals must have a powerful, dedicated CPU, buffering capabilities, and some form of networking built in.)
Can a MacWorkStation-to-X Window System Interface Be Written?
An X server and a remote X client application communicate over a network using a "reliable byte-stream" built on top of a network protocol, such as TCP-IP or DECNet. The same kind of mechanism is used by MacWorkStation to communicate with an IBM mainframe (but the protocol used and many other details differ from X).
The X protocol provides for vendor-specific extensions (a trap door), which allows clients to access special functions in the server. It might be possible for a Macintosh-based X server to offer an extension that offers clients use of Macintosh Toolbox components (like MacWorkStation), but we don't know of any plans to implement such an extension.
Is X Window System like PostScript?
X and PostScript are similar, because they both are used to generate graphic images on bit-map devices (in this sense, QuickDraw is also similar). However, X and PostScript have very different "imaging models." X regards the screen as a rectangular collection of pixels--each may be individually addressed by giving its horizontal and vertical coordinates (like QuickDraw). Lines, curves, and shapes are specified in terms of these device-dependent coordinates.
PostScript, on the other hand, hides many of the device-dependent details (like discreteness of pixels) and gives the programmer the illusion of painting on a canvas in any convenient coordinate system. The PostScript model is, in many ways, richer and easier to use. In addition, PostScript is a true programming language and allows for concise and compact expression of complicated graphic images.
The Sun NeWS window system is based on PostScript. A NeWS application is a collection of PostScript procedures that are sent to a NeWS server (perhaps remotely via a network connection). The server interprets the PostScript procedures and renders graphics in a window on the display's bit-map screen. NeWS extends PostScript by allowing interactive input: the PostScript procedures can respond to user input--keystrokes, mouse motion, and mouse clicks. Some of NeWS is written in PostScript (after all, PostScript is a programming language). In particular, the NeWS window manager is a PostScript procedure.
How Is X Window System Comparable to Display PostScript?
Display PostScript (licensed by Adobe) lets a PostScript procedure render graphics on a bit-map screen (in the same manner as a LaserWriter with its built-in PostScript lets a PostScript procedure render graphics on a sheet of paper). Display PostScript differs from NeWS in that it does not take into account interactive input. X and Display PostScript can be used together: Display PostScript is a front end that accepts a client's PostScript procedure and then issues commands to X causing the appropriate graphics to be drawn in an X window.