Its interesting that scalability was brought up in relation to...Linux. Well. I look at a computer such as SGI's Altix 4000 (here: http://www.sgi.com/products/servers/altix/4000/). It supports up to 512 processors under one instance of Linux and as much as 128TB of globally shared memory, and Petabytes of disk storage (kind of like 512 servers all at once). The alternatives listed? Not on this machine? How about the computers at top500.org. The current list of the 500 fastest supercomputers in the world. The database that lists operating systems is here: http://www.top500.org/stats/28/osfam/. Tens of thousands of processors (all at one go). Is that what was meant by scalability? What about the Department of Homeland Securities use of Linux, or the US Navy, Air Force, NSA, NASA, etc. How about the big Hollywood studios? Is that what is meant by 'scalability'? Please please let me know if you want links. I have oodles of them.