How can I allow my kernel to save data. Example: Going into a notepad and clicking file and save.

P.S - When developing a 16 bit kernel, should I use C or Assembly. If C what program should I use to compile C?

from the questions your asking it sounds like you should learn programming first. the best advice I can give is to exploit debugging tools in software such as Visual Studio to learn what the assembly for applications look like (and as a tool in learning programming in general) then move into assembly and OS development.

when you write your own OS the only tools you'll have are the ones you write yourself. if you don't fully understand what you're doing you won't be able to push forward.

- Stefan

You are going to have to make a file system driver first. You can choose any file system that you like and then make some code to implement it. At some point you will have to use assembly because C can't do all the things needed to access the hardware or the special CPU settings and mode control. So if you take the path of C then you have to mix it with assembly. And if you take the path of assembly then you can use just that and ignore C completely.

The C vs ASM choice can only really be answered by you - what requirements/goals/design are you going for?

For C there are only a few older/less-known compilers that support 16bit code generation such as Turbo C or OpenWatcom (there are others).