Access
On Sun SPARC systems, the Open Firmware interface is displayed on the console terminal before the bootstrapping of the system software. If a keyboard is connected, the main video display will be used as the console terminal and Open Firmware can be re-entered at any time by pressing Stop-A (L1-A) on the keyboard. If no keyboard is connected, then the first serial line on the system is usually used as the console and Open Firmware is re-entered by sending a "Break" on the serial line. While the system software is running, various Open Firmware settings can be read or written using the eeprom command.
On a PowerPC-based Macintosh, the Open Firmware interface can be accessed by pressing the keys ⌘ Cmd+⌥ Option+O+F at startup. Intel-based Macintoshes do not use Open Firmware; they use Extensible Firmware Interface, following Apple's transition to Intel processors. Also, early versions (before the PowerBook 3400) connect Open Firmware's input and output to the Modem port by default. This functionality is generally only used by developers or troubleshooting I.T. personnel; for common users, the Mac OS X operating system provides a high level graphical user interface to change commonly used Open Firmware settings. For instance, it is possible to specify the boot disk or partition without directly using the Open Firmware interface. Other Open Firmware settings can be changed using the nvram command while the system software is running.
On Pegasos, the interface is accessed by pressing Esc at startup.
On IBM POWER systems, Open Firmware ("ok" prompt) can be accessed through the SMS Boot Menu. SMS Boot Menu can be accessed by pressing 1 or F1 during the boot sequence, after hardware checking, and just before the OS boot.
On the OLPC XO-1 laptop, open firmware access requires a developer key, that can be obtained after registration with OLPC. After installing the key, upon each power-on, the boot countdown can be interrupted with Esc (the upper left key) to get to the Forth prompt.
Read more about this topic: Open Firmware
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