How Can I tell which PC Operating System?
The easiest way to tell which operating system on a PC is to click on the start button and read the text on the left hand side of the menu. If this is not available then right mouse on my computer and select properties this screen should tell you. If your machine will not boot that far try turning it on and reading as the machine loads the operating system.
How Can I tell which Macintosh Operating System?
From the finder click on the apple in the left hand corner and select about this computer. The finder is where you can see icons of your hard drive. This screen will tell you which OS. If your machine will not boot that far try turning it on and hold down the shift key until the machine and see if it will boot to the finder. If your machine will not boot that far try turning it on and reading as the machine loads the operating system.