CNET News.com: Commentary: Linux’s murky prospects

“…In short, Linux yields the most savings, compared
with Unix or other operating systems, where Linux servers have a
dedicated function, such as Web server, caching or proxy, and where
the environment can be replicated over many servers–to hundreds or
thousands in a server farm, for example.

That means Linux does best in highly replicated arrangements as
a low-end extension to Unix. As the software stack running on top
of Linux becomes more complex or comprises commercial proprietary
elements, Linux’s cost advantage over Unix will shrink.

At Amazon, Hewlett-Packard’s Unix OS, HP-UX, still hosts the
business-critical database and enterprise applications. It remains
unclear whether Linux will maintain similar cost advantages at the
high end; Linux could prove even more costly than Unix in these
environments, depending on the factors listed above.”

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