From the opening chime to the login window, there is quite a bit of activity going on behind the scenes during the Mac OS X boot process. Nowadays with newer versions of the OS, that process takes hardly any time at all. Old timers will remember the slow march of system extension icons in the paleolithic age, pre-OS X.
This page at kernelthread.com, “Mac OS X System Startup” uncovers the after-hitting-the-power stuff. A sample from the beginning:
- Power is turned on.
- Open Firmware code is executed.
- Hardware information is collected and hardware is initialized.
- Something (usually the OS, but also things like the Apple Hardware Test, etc.) is selected to boot. The user may be prompted to select what to boot.
- Control passes to /System/Library/CoreServices/BootX, the boot loader. BootX loads the kernel and also draws the OS badges, if any.