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LPC: 25 years of X

Oct 08, 2009, 18:34 (1 Talkback[s])
(Other stories by Jonathan Corbet)

"The version of X we know today is X11. There were nine predecessor versions (one got skipped), but the first version to escape widely was X10, which was released in 1986. Companies were shipping it, and the vendors which [Keith Packard] formed the X Consortium were starting to think that the job was done, but the X developers successfully pleaded for the opportunity to make one more "small" set of revisions to the X protocol. The result was X11 - a complete reworking of the whole system - which was released on September 15, 1987; it is still running today.

"There was a wealth of new ideas in X11, some of which made more sense than others. One of those ideas was the notion of an external window manager. In X, the window manager is just another process working with the same API. This approach helped to create a consistent API across windows, and it also made it possible to manage broken (non-responding) applications in a way that some other systems still can't do. On the other hand, the external window manager created a lot of on-screen flashing - a problem which still pops up today - and it does not work entirely well with modern compositing techniques, getting in the way of the page-flipping operations needed to make things fast.

" The use of selections for cut-and-paste operations was another early X11 innovation. With selections, the source of selected data advertises its availability, and the destination requests it in the desired format. This mechanism allows data to be selected and moved between applications in almost any format. Unfortunately, the "cut buffer" concept was left in, so applications had to support both modes; the fact that Emacs was not updated to use selections for a very long time did not help. The existence of multiple selections created interoperability problems between applications. On the other hand, the selection mechanism proved to be a very nice foundation for drag-and-drop interfaces, and it handled the transition to Unicode easily."

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