Mac OS X for hackers

What is Mac OS X? – a hacker-friendly answer [null].

Full of natty bits like the following:

It is worth noting that pressing T while your Mac powers on would boot it into what’s called the FireWire Target Disk Mode. Essentially, your Mac becomes a fancy external FireWire disk drive.

XNU’s Mach component is based on Mach 3.0, although it’s not used as a microkernel.