What is the difference between Unix-like systems and non-unix systems?

Question

Operating Systems

Here is the site rus-linux.net/MyLDP/kernel/toyos/sozdaem-unix-like... Complete writing of the unix kernel operating system. Probably the most elaborate and detailed series of articles I've ever seen.
But everything is there from scratch, I thought, like you need to connect some kind of library, or like there is a Unix framework, and like there already write features.
What's the question. Everything is written from scratch there, the loader, ... there are no imports, libraries or anything else. THAT is pure code, Why is the kernel unix-like there . THAT is any kernel of the operating system that you personally write, will unix be similar? Or how?
What should be the attributes of a unix kernel, or rather the reverse question is how to write a non-unix like kernel .
Google does not provide a clear answer to the question

Answer 1

Read what is https://ru.wikipedia.org/wiki/POSIX
In short, this is a standard that describes the requirements for the operating system.
If the operating system is written in such a way that it supports this standard, then a ready-made program can be compiled for it from existing code, and not written specifically for it from scratch.
What frameworks? What libraries - OS is practically the most low-level that is. Therefore, yes, clean code, using the BIOS functions.

What should be the attributes of the unix kernel, or rather the reverse question is how to write a non-unix like kernel.

You invent what you want and write - it will not turn out like a Unix.

Answer 2

To practice, read here
https://forum.ixbt.com/topic.cgi?id=48:12447
The advantage is that relatively simple systems cannot be compared with a general-purpose OS.
https://habr.com/ru/post/249273/
As for comparisons, this is a thankless task. Unix like OS is a very broad concept.
https://en.wikipedia.org/wiki/Comparison_of_operat...