Your login shell can be changed by using the chsh or ypchsh command.
There is no "default" Unix shell. Different Unix vendors shipped different shells.
CD /
A Unix shell can be obtained in Cygwin, a Unix compatibility layer used to compile Unix programs and run them on Windows. Microsoft also makes a shell known as "Windows PowerShell" which incorporates more Unix-like features than the standard command prompt.
The first shell was 'sh', the Bourne Shell
The a default Unix shell is the shell that comes with and is activated initially with your distribution of Unix. The shell is essentially the program the runs the command line interface allowing someone to interact with their computer. Some examples are the Bourne-Again shell (bash) or the Bourne shell (sh).
Use the 'chmod' command to change permissions on any file. Note: you have to be the owner (or the superuser) to do this.
Unix has the following categories of users: Superuser - root account, can do anything on the system ordinary user - has no special privileges restricted user - is restricted in what they can do in the shell and programs they can run.
The Korn shell.
The Z shell is a Bourne-compatible shell for Linux and Unix systems.
You should be able to download the Unix Services for Windows, version 3.5, from Microsoft (free). There are other shell emulators that are available for Windows, which would allow you to use Unix type shell scripting without installing any additional OS. Your question about "virtual UNIX" is unclear ..
Use the shell variable PS1 to set the command prompt to whatever you need.
shell