For any Mac made in the last 10–12 years, you typically do not buy a physical "piece" of software.
: Recent versions like macOS Tahoe are free downloads via the Software Update section in System Settings. buy osx
: Highly sought after as the final version to support PowerPC Macs. For any Mac made in the last 10–12
: Around $130 at retailers like eBay - pcmonde. buy osx