In how many ways linux is different from unix like kernels?

view full story

http://unix.stackexchange.com – Unix like kernels were in picture from a long time. But due to its limitations it is not as successful as linux kernel. What are those limitations. Basically I want to understand the fundamental/advanced points which describes the differences between Linux kernel and Unix like kernels? Please be specific to Linux and Unix internals only. (HowTos)