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The BSD personality: how XNU pretends to be Unix
Processes, file descriptors, signals, sockets — the FreeBSD-derived layer that sits on top of Mach and makes macOS pass POSIX.
bsdposixkernelxnu
Virtual memory in XNU: pmap, the VM map, and the compressor
Every macOS process gets a private address space it can't possibly afford. Here's how XNU gives it one anyway — pmap, vm_map, the compressor, and jetsam.
virtual-memorykernelxnucompressor