This is true of the actual hardware that implements the control logic in software running of specialized hardware that requires fast response to real time events.  However, many of these systems use Windows servers to collect, monitor and present an interface to the user world.  Under these &quot;monitoring&quot; conditions the support servers can be virtualized, and in fact, Emerson the makers of DeltaV, released a white paper stating that their Window support servers can be virtualized over 2 years ago.  In many other cases the vendor&#39;s control loops and time critical calculations are performed in hardware that feeds data to and from these monitoring servers.  In the case of Allen Bradley PLCs, they actually have a software version of the operating system that emulates on Windows and will drive their hardware via serial connection.  Much control software development is actually performed on VMs as both Allen Bradley and Emerson both Winmdows software emulators that allow development and simulation off line.  My former company has been doing this for over 10 years using VMware on laptops.  As processor speed increases this will only narrow the gap of dedicated hardware vs virtualized hardware emulated in software.  Now, you might not be able to run 10 VMs on one server and bet the required performance, but the day is coming as the cost of supporting these one off systems becomes prohibitive.<br>
<br>Paul<br><br><div class="gmail_quote">On Sun, May 15, 2011 at 11:22 AM, Tom Horsley <span dir="ltr">&lt;<a href="mailto:horsley1953@gmail.com">horsley1953@gmail.com</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div class="im">On Sun, 15 May 2011 10:24:41 -0400<br>
Paul Lambert wrote:<br>
<br>
&gt; The reason I ask these questions is there are many companies in the control<br>
&gt; industry that continue to build their own proprietary hardware that is very<br>
&gt; expensive<br>
<br>
</div>Most process control systems need reliable real time behavior (consistent<br>
latencies and wot-not). Just try to get a virtual machine to keep something<br>
as simple as the time of day clock correct and you&#39;ll discover how<br>
useless virtual systems are for real time behavior :-).<br>
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