Linux got a kernel.
Windows got a kernel.
Mac OS got a kernel.

A kernel is just a word for the very innermost tasks a Operating System. These are managing the memory, detecting and serving all hardware pieces and take care about the rights.

These tasks have to be done no matter how the resulting system is called.

If you write "shellcode" in windows, you can execute this code on a Linuxbox.
If, and only if this code is written for a linux shell.
Linux has a load of different shells. "bash" "dash" "ksh" "tsh" just to name a few.

If yxou are writing "shellcode" for the "powershell" you can run this code in windows as "powershell" is a windows shell. It won't run on a linux box.

If you install "cygwin" in windows, you are able to run real Linux shellscripts.
If you install "wine" on a Linux box, you are able to run Powershell scripts on Linux.
But in this two cases they run in a kind of simulation of the other operating system.

So again: You can write "shellcode" with every editor on every operating system.
But the written code is only executable on the corresponding platform.

Thanks for the information. But i have some more doubts.
You said that shellcode may be written in any language.That is,can i write the shellcode in c,c++,jave etc.??
And, Does an OS has more than one shell?
And you said that "Windows has the CMD shell (when running cmd.exe)."
Does there is no shell without running CMD in windows?

Again, read the Wikipedia article about shellcode.
Then read this LQ rule:
That means asking questions on those subjects, too.

Give this on smashing the stack a read Mr. Cracker. I don't know if its up to date. This article came out a while ago. It's written by Aleph one and hosted by Insecure.org

I think the stack has a precaution enabled called randomization built in now. Your code would need an nop sled/padding added to work correctly or if your testing your own code you could disable stack randomization. To disable the SR-->
You would need the basics of assembly at the very least. It can become quite complicated! Interesting topic though!