The Unix underpinnings, frameworks, and platform security model behind Apple's desktop OS.
Released August 28, 2009, Snow Leopard was the first Mac OS X built exclusively for Intel Macs - a deliberate stability release, not a new-features showcase.
On May 18, 2007, Leopard on Intel Macs became the first BSD-based OS to earn Open Brand UNIX 03 certification, making 'Mac OS X is Unix' a certified fact.
How the App Sandbox confines what an application can access by default, and how entitlements grant it specific, narrow exceptions.
What SIP protects, how it's enforced below the level of the root user, and the legitimate reasons to disable it temporarily.
How mdworker, metadata importers, and Spotlight's index let macOS answer file searches in milliseconds instead of scanning the disk on demand.
How Virtualization.framework exposes Apple Silicon's hardware virtualization support directly to Swift applications, without a third-party hypervisor.