Pixar has been traditionally big on using using Linux servers for their RenderMan Pro Server software. Even though the company was developed by Steve Jobs and later sold to Disney, Mac servers as cluster nodes are not widely used, according to Computerworld on Friday. There are multiple reasons for that.

Eric Lai recently wrote about how Microsoft is moving aggressively into compute clusters, and after questions from readers, looked deeper into the situation regarding Linux and Mac OS X

While RenderMan does indeed run on both Linux and Mac OS X, Linux is the preferred platform according to one the authoris sources. [RenderMan Server is] "certainly used extensively on OS X workstations...very few people run RenderMan on OS X clusters," the source said.

"Technically, OS X is very well suited [for clustering] but it does not seem to have made much headway," the source added.

One reason cited for the Linux preference is that Xserves are much more expensive than white box Linux servers. However, another reason not cited in the article is that cluster operations often require subtle and technically difficult changes to the Mac OS X kernel. This reporter is has been exposed to situations in which changes required for better cluster operations at Apple took a back seat to consumer oriented concessions. On the other hand, experienced computer scientists can simply recompile the Linux kernel to suit their needs when necessary.

That tinkerability of Linux is great for rendering and scientific computing but bad for corporations who want a steady, solid, immutable kernel for stability in their architecture.

Microsoft has plans to move into the small cluster space with "Windows HPC Server" but is likely to be greeted with the same reaction as Mac OS X because of its closed architecture.

So long as PC boxes are cheap, Linux is free and tinkerable, movie studios and scientists are generally going to use Linux as their preferred large cluster platform. Apple knows that and isnit likely to change its products, tending to focus more on the small business and scientific desktop where the advantages and ROI of Xserve and Mac OS X shine.