based operating systems?
By default, the other free OS’s aren’t SMP very capable out of the box–Solaris is. So, one single CPU system, Solaris has a fair amount on un-necessary overhead–which slows it down a bit. Because the other OSes don’t have this capability, or at least don’t use it to full advantage, they have a bit of a performance advantage on a single CPU machine. This advantage disappears when you start adding processors.