> The proper term is "zombie", I believe. This is lock-in schemes at work. Think War of Currents: AC distribution networks won back in XIX century yet some customers still bought elecricity from DC networks in XXI century!
Yeah, inertia is a powerful force :)
> UNIX may linger for similar amount of time, but it's relevance is the same: existing customers keep the thing alive, but there are few (if any) new users.
I don't think it will last quite as long as DC current, i.e. even 20 year old technology is woefully out of date, but still lurks in some dark corners of data centers. I have never seen one, but I heard stories that some places keep some PDP hardware alive to run certain jobs. My own experience closest to these stories was some BS 2000 mainframe sitting in the corner of a data center to do certain jobs, no idea what exactly, but I counted myself lucky I had nothing to do with it.
As long as Unix vendors make money, they will sell and support it. There are really only three vendors left that matter (IBM, Oracle, HP) since Irix went into really deep maintenance mode and Tru64 is officially no longer supported. The BSDs do not really matter commercially in that market, but they are important for the custom storage and routing operating systems for companies like Netapp, Isilon (bought by EMC recently) and Juniper to name a few. Illumos is competition to the 'storage BSDs' and I would personally like to see it prosper since it is at least open source while the filesystems developed by Netapp and Isilon are not. Linux is certainly also used more and more in storage applications, so it will be interesting to see how commoditization will affect that market. James Bottomley has been giving talks on the economic forces of open source, i.e. look at LinuxCon Japan 2012 iirc for a recent example, and in those he argues that products that face commoditization tend to have the aspects that aren't value added parts open sourced. And the filesystem and routing function in operating systems seem to be at this point, i.e. five or ten years ago a storage box was big bucks, these days you can build one with open source without much trouble. So there has been price pressure on commercial vendors since you really start to have trouble to charge extra for a dedup feature in your array if you can just get an open source one. There is still plenty of gear to be sold in the high end, but I am certain places like Netapp fell the pressure.
To get back to Unix: I personally think that HPUX will be the first to go of the three left since Itanium's future looks more than a little bleak if you have read the discovery documents Oracle published . HP has attempted to port HPUX to x86-64 twice ( and ), but killed it again and again, so I think it will be the first to go as Itanium hardware support fades. Solaris has x86-64 and IBM seems to be able to sell enough Aix on Power despite the lack of workstation models which traditionally has indicated that a platform is in trouble.
And in the end what matters most is applications, which I suspect is the reason that the x86-64 port of HPUX was killed, i.e. why port to HPUX on x86-64 if you can run the software on Linux? If you look at the articles you will see that HP wanted to offer RHEL 6 compatibility so that Linux apps can run. I have no idea how they wanted to do it, i.e. visualization, kernel run time support via personalities or whatever. And this is really the issue with Illumos, to get back on topic, i.e. will software vendor support commercial software on it? I doubt that it will happen for a significant number of software packages and Oracle will certainly be hostile to them since the uname is still identical to Solaris. I am sure plenty of that unsupported software will run, but I do not think many companies will take a gamble to run their Oracle DB on a Illumos derivative :). Even free software project have started to have issues, i.e. there was a patch on the Mesa list to disable some features on OI/Illumos due to missing headers that worked perfectly fine on Solaris 11. It didn't go in. I have seen similar conflicts with patch sets to the user space code to OFED for example, too.
In the very end the weakness of the Illumos/OI community can be IMNSHO demonstrated via two issues: (1) no support for Sparc (2) the Illumos port of KVM does not have AMD support, i.e. it is Intel x86[-64] only, roughly two years after it was released. I wish them luck since I believe they will need it.