prodz & others (including myself),
put them this way. every branded unix system is likely to be dependant on the hardware supplied together with the os. for example ibm aix runs best only on ibm rs6000, sun solaris on sun sparc-based, and hp-ux on hp9000 machines.
this is one of the motivation for linux father "tuan guru" linus tolvard to create a unix system which runs on intel-based machines - the ibm-compatible personal computers.
correct me if this remark misleads.