No, mach is a microkernel, like L5. It was developed for the purpose of replacing the BSD kernel, by having a small amount of functionality in the kernel itself, and the rest of the BSD-compatibility layer implemented in user space. macOS' frameworks are then a layer on top of that.
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
IIRC most of the BSD compat was moved to kernel space for performance reasons (either just on macOS, or the version of Mach they built on top of)