Leopard requires a minimum of 867Mhz

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Version 10.5: "Leopard"

Mac OS X Leopard was released on October 26, 2007. Apple called it "the largest update of Mac OS X". Leopard supports both PowerPC- and Intel x86-based Macintosh computers; support for Macs with the and at least 512 MB of RAM toG3 processor was dropped, and Macs with the G4 processor required a minimum clock rate of 867 MHz  be installed. The single DVD works for all supported Macs (including 64-bit machines). New features include a new look, an updated Finder, Time Machine, Spaces, Boot Camp pre-installed,[49] full support for 64-bit applications (including graphical applications), new features in Mail and iChat, and a number of new security features.

Leopard is an Open Brand UNIX 03 registered product on the Intel platform. It was also the first BSD-based OS to receive UNIX 03 certification.[2][50] Leopard dropped support for the Classic Environment and all Classic applications,[51] and was the final version of Mac OS X to support the PowerPC architecture.