Comment by egberts1

The UNIX libcompat (a compatibility library for older UNIX functions) was integrated into Mac OS (specifically, macOS) rather than directly into Mach OS.

Here’s the breakdown:

• Mach OS refers to the Mach microkernel, which primarily focuses on low-level system functions such as task scheduling and memory management. It is not a full-fledged operating system, and thus, libraries like libcompat, which are higher-level UNIX compatibility libraries, would not be integrated directly into the Mach kernel itself. • Mac OS (particularly macOS, formerly OS X) is a complete operating system that includes the Mach microkernel, the BSD layer, and various other components. macOS has a strong Unix heritage, and libcompat is part of the broader Unix-like environment included in macOS to support legacy Unix APIs and applications.

Thus, libcompat was integrated into macOS (or its predecessor, NeXTSTEP) as part of its Unix compatibility layer, rather than into the Mach kernel directly