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APFS clones and snapshots: the kernel calls that make them work
clonefile, fclonefileat, fs_snapshot — three syscalls that let you copy 50 GB in 50 milliseconds. Here's what happens under each one, and what doesn't get copied.
Apple Silicon and XNU: APRR, unified memory, AMX, Rosetta 2
What changed in XNU when Apple shipped its own ARM silicon — P/E cores, APRR page-permission switching, the AMX matrix coprocessor, and Rosetta 2.
DriverKit: how Apple is moving every driver out of the kernel
Same IOKit object model, userland process. Why kexts are dying, what DriverKit gives you, and how a USB driver actually crosses the boundary.
macOS security architecture: signing, sandbox, SIP, TCC
Six interlocking layers — code signing, AMFI, entitlements, sandbox profiles, SIP, TCC, and the SEP — that together decide what code is allowed to do on a Mac.
Signals in XNU: where POSIX semantics meet Mach reality
POSIX says signals are per-process. Mach says everything is a thread. Here's how XNU bridges the two — pending masks, delivery threads, the AST mechanism, and exception ports.
The XNU scheduler: bands, QoS, and how Mach decides who runs
Real-time, fixed-priority, timeshare, idle — four scheduling classes, 128 priorities, and a QoS layer on top. Here's how XNU picks a thread to put on a core.
Inside APFS: copy-on-write, snapshots, and the sealed system volume
Apple File System, the format under every modern Mac: how it lays out blocks, how it gets snapshots almost for free, and why your /System is read-only at the cryptographic level.
IOKit and the driver model: how a Mac talks to its hardware
Embedded C++, an object tree, and matching dictionaries — IOKit is how every driver on macOS gets loaded, paired with hardware, and called.
Mach ports: how every macOS process actually talks to another
Tasks, ports, messages, and rights — the IPC primitive that quietly carries every IPC on your Mac, from XPC to drag-and-drop.
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.
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.