How does Itanium work?

[Thomas Schler_1]

Hi,

I wonder, how the different OS's can be executed on an Itanium processor.

About three years ago, when I first heard something about Itanium at an HP meeting, one said Itanium could execute different OS's at the same time, i.e. parallel. This would mean you would be able to execute HP-UX and Windows at the same time on one processor. And if Windows goes down for some reason (too many reasons in my opinion), this would not affect the running HP-UX. Meaning that HP-UX is running while Windows goes down and re-starts later, all on one processor. Of course, I asked some questions about that, but the speaker didn't know any detail (I don't know if he still works at HP).

At that time, I didn't believe that and I don't believe it, today. But I don't know. The documentation I have is not clear enough.

But to be sure, tell me if Itanium really executes two OS's at the same time, or if you have to choose which OS you want to run before booting (that's what I believe).

[Rodney Hills]

A purchased product from HP is "vpar" (virtual partitions). It allows you to partition your hardware for the different operating systems you wish to run.

-- Rod Hills

[Patrick Wessel · Accepted solution]

Thomas,
I'm not aware of any plans to implement several operating systems on a single CPU. But If you have a system with multiple partitions (like the IPF successor of rp7410, rp8400 or SuperDome) you are able to run different independent OSs on the different partition.

[Mark Landin]

Actually, a CPU can only "execute" one O/S at a time. However, using various technologies, a computer system can have two or more O/S's running at the same time ... the CPU just switches between the two just like it switches between different tasks.

One key feature Itanium has that is of special interest to us HP users is that it really understands two different instructions sets ... the native IA-64 instruction set, which was researched and developed by HP (and licenses to Intel for manufacture and marketing), and the PA-RISC instruction set. THis is great news for us, because it means that our PA-RISC programs will run on Itanium without being recompiled. On the other hand, programs compiled for the Pentium processor line, for instance, will NOT run on Itanium ... those applications will need to be recompiled with an IA-64 compiler. This means that your favorite Windows application will not run on Itanium until the vendor releases an Itanium version of it. Your HPUX applications, however, will most likely run on your Itanium server without any problems.