Open Firmware

Open Firmware, now also known as OpenBIOS, is hardware-independent firmware (computer software which loads the operating system) initially developed by Sun Microsystems for use in their -based workstations and servers. It was described in 1275 and adopted by PowerPC-based systems such as. However, IEEE 1275-1994 was not affirmed by the Open Firmware Working Group in 1998 and has since been withdrawn.

Open Firmware may be accessed through its, which is based on the.

Apple and Open Firmware
Apple Computer adopted Open Firmware with its PCI-based Power Macintosh models, starting with the Power Macintosh 9500 in 1995. For such models through the beige Power Macintosh G3, the classic Macintosh Toolbox was stored within the boot ROM itself as an Open Firmware device. Thus, they are still classified as Old World ROM systems. Starting with the first iMac G3 in 1998, a bootloader would instead load New World ROMs from the boot drive. The Open Firmware interface can be accessed at startup by holding down the      keys.

Booting
Open Firmware on PowerPC Macs can boot from a drive volume partitioned through an Apple Partition Map (APM). However, it is unable to support booting from drives partitioned through a GUID Partition Table (GPT) favored by Intel-based Macs, though such volumes can be mounted and accessed.

Version history
Open Firmware versions are not indicative of release order as Apple tended to release newer firnware in portable PowerPC notebooks than desktop models. Some firmware updates were released with a confusing naming convention where it was unclear whether the number referred to the version of the update itself or the resulting firmware version after the update.

Discontinuation
Starting in 2006, Apple phased out its use of Open Firmware in favor of EFI (Extensible Firmware Interface) during its transition to Intel processors.