Question

Hello!

I often encounter information about the X11 server.
Sometimes the version is written as 1.6.x, sometimes as 7.4.x.
However, in both cases, same product seems to be referred.

Why these are such different notations?

Is there a mapping, or an "algorithm" to map these different notations?

Answer 1

The version numbers refer to different things..
7.x refers to the "X window system" (X11) version. In other words, the version of the specs that define the protocols being used and things like that.
1.x refers to the "X.Org" server version, an implementation of the X11 specification.

Wikipedia has a table that could be used as mapping between the two.

Answer 2

They refer to two related things:

1. The X.org version, which is at 7.x. This is also the X11 spec release version.
2. The X server component of X.org, which is at 1.x version

The naming isn't terribly brilliant and causes some amount of confusion, but this are effectively the two versions being referred to.

$ dpkg -l xserver-xorg xserver-xorg-core
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Cfg-files/Unpacked/Failed-cfg/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
||/ Name                      Version                   Description
+++-=========================-=========================-==================================================================
ii  xserver-xorg              1:7.4~5ubuntu18           the X.Org X server
ii  xserver-xorg-core         2:1.6.0-0ubuntu14         Xorg X server - core server

See this bug report which addresses this your question: xorg: /usr/bin/Xorg -version gives a wrong answer. From the report:

X.org is modular now. The version number of Xorg does not mean much, it's sort a tag on lots of components. Right now, unstable contains many components from 7.2, a couple from 7.1 to be updated soon (including xorg/xserver-xorg/x11-common), and some already more recent than 7.2 (inclusing xserver-xorg-core).

The core component of X.org is the X server (aka xserver-xorg-core, already 1.3.0 in unstable and upstream). This is why you see 1.3 here.

Answer 3

Peter Hutterer, one of the X.Org developers and the release manager of the Xorg server 1.7 release, posted an explanation of this on his blog today: X11R7.5 released - but what is it?