Weta Digital, the special effects company behind the Lord of the Rings film trilogy, got great value out of a switch to Linux but found support and memory problems a "can of worms".

Weta says it achieved about twice the performance for half the cost in rendering its mix of CGI and filmed images when it changed to Linux on Intel processors.

The traditional platform the Wellington film graphics house had been using for four or five years was built of Silicon Graphics Mips-based processors running SGI's Unix variant, Irix. Three years ago, looking at getting the biggest bang for its buck, Weta became aware that some of its software suppliers, such as Nothing Real, Pixar and Alias Wavefront, were supporting Linux.

It settled on Intel-based SGI processors -- 700MHz Pentium 3s -- running the open source operating system.

The new operating system "did open a can of worms" says Weta's Milton Ngan.

"The hardware is cost-effective, but the onus of support fell on the people here. During film one it became obvious we didn't have the resources, so for film two we had to purchase support from a vendor, which was IBM."

Porting inhouse-developed rendering and simulation software was another problem.

"Linux was not designed for large processes and large files; it didn't support enough memory."

There were still a variety of other processors in the company, which had to be brought into the Linux fold too.

"We had to be careful about detailed differences in the motherboards, which Linux addresses in native mode."

The risk was particularly high when going beyond the 4GB memory barrier.

"Fortunately, with open source we could get right inside the system to the C library calls," says Ngan, "though for the size of the team we had at the time, expertise in that area was pretty thin. But when I was at university, I'd spent some time working with Linux and BSD. It took time, but it wasn't overly challenging. It's not something you'd throw at a programmer with less experience, though."