Hi dears I'm fazal khan
I have dell optiplex 270 operating system in whcich I would like to have two "OS" in one hard drive I don't know the process there I'm asking you assist me in this issue . ThAnks for assistance

Regards
Fazal khan

Yes and no.

Yes it is more than possible to dual, or even triple, boot your machine to numerous OSes.
No, it is not advisable that multiple OSes are installed on the same partition.
That being said you can use different partitions of the same physical disc.

Yes it is what two Operating systems do you want? Running Linux and Widows together are relatively easy most Linux installers will detect the installed Windows OS and give you the choice to dual boot. Debian and all the Ubuntu Family of Distributions make it easy to set up a dual boot and guide you through the installation. If you want to run two versions of Windows you will have to make two partitions and install one version then the other you will get a prompt to select the version you want to use at start up.
You can also install Virtual Box and run the second OS on a virtual machine giving you access to both operating systems with out having to reboot to switch.