If you take a look at the TOP500 list for the fastest computers in the world, it is dominated by Linux. Actually 98,3% af all computers is running Linux. That is 469 of 500. And in a couple of years there might NOT be any more than 1 or 2 Windows computers on the list. If you go back to last years Linux share it was 91,8% – so Linux continues to dominate the worlds market of the fastest computers and servers.
Microsoft has a fast computer on the list as number 10. It is a Windows HPC Server 2008. A part of the reason is that Microsoft cant deliver any programming tools for developing fast computers. When talking about fast the fastest servers is running more than 1 petaflop means 1026 quadrillion calculations per second. Intel does hold the record of the processors used as 75% of the TOP500 is from Intel. The other processor vendors is Sony, Cray, AMD and Sun.
In the coming years we will se more and more Cloud Computing systems which works as supercomputers because it is one of the cheapest ways to create a supercomputer. Actually you may use standard 19″ 1U Rack server to bundle many of these to a SKY which is the benefit of Cloud Computing. If you take 42 of these with 3 GHZ and 10GB memory and 4 TB disks, you will have SKY which have a 126 GHZ CPU, 420 GB Ram and 168 TB hard disk. The price for such a Rack Cabinet with 42 rack servers would be below 100.000 dollars.
Why is Linux so popular? First of all Linux is having around a 73% market share in the server market which is used in datacenters and hosting centers. Next Linux is of course free AND Open Source, but also scalable from start, so you may start with 1 rack server and have about 10 servers up running the next day, with Cloud Computing and / or Clustering with Automatic Process Failover and Load Balancing.
Check out the TOP500 list: http://www.top500.org/project/introduction