Go to the apple menu at the upper left side of your desktop screen. Click on "about this Mac". The screen that pops up will tell you the operating system that you are running.

You may download a freeware called Mactracker that list all the Macs with their specs, original installation OS and much more.

http://mactracker.dreamhosters.com/

It depends when you bought it. Some PBG4's came with Panther (OS X 10.3), most came with Tiger (OS X 10.4), although it is capable of running Leopard (OS X 10.5).

To find out which one you are running, see Tyler Bly's Answer. (Go to Apple Logo in upper left hand corner and select About this Mac from the drop menu).

If you haven't upgraded it will tell you on the box.

If you have (or not kept box) go to the  menu in the top corner of the screen and select about this mac.

If you have the feature Expose you have minimum panther (10.3)

If you have spotlight in your top right corner it is minimum Tiger, also if you have Automator it will be at least Tiger (10.4).

If you can press spacebar when selecting a photo, music, movie, document e.t.c, and view a preview (Quicklook) then you have minimum leopard (10.5).

If you have several windows of one application open and click and hold the application icon in the dock; if all the windows appear in Expose you have Snow Leopard (at time of writing) maximum (10.6). However, this seems unlikely as Snow Leopard requires an Intel processor)

I have a PowerBook G4 15" 1.5GHz 512, 80GB and it came with 10.3 and I now have it at 10.3.9 so that I can continue to run Classic for an Adobe Suite that I own.

Hi, I think I might have a piece of the puzzle. Where does classic become unsupported and how do I get back there. I have software that is old and some scanner options not supported in os 10.5.8.

classic becomes unsupported as of Leopard 10.5, Classic environment will no longer be installable or usable, however you can run classic in Tiger 10.4 - 10.4.11 and software is still being compiled and released on the web which supports OSX Tiger as opposed to less software being developed for the much older 10.3 panther. david