programming models in writing o.s

There is no a single model of the level you mean even in a single OS.
The programming models used in new systems are too different to make any sensible answer.
I think if you aim to write you own you need to make your own decision — the less you look behind at existing OS, the more valuable might be yours (in case of success, of course).

Linux is not object-oriented, probably as every Unix (but I cannot guarantee that), but some others are deeply object-oriented (notable example is Singularity http://en.wikipedia.org/wiki/Singularity_(operating_system)[^]).

Most common classification of OS is based on the modularity concept, especially relative sizes of the kernel and how independent they are (Microkernel, Hybrid kernel, Monolithic kernel, etc., see http://en.wikipedia.org/wiki/Micro_kernel[^]).

—SA