New World ROM
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New World ROM Macintoshes are the Macintosh models that do not use a Macintosh Toolbox ROM on the motherboard, but instead use a pure Open Firmware implementation similar to Sun Microsystems' OpenBoot; these machines load the Toolbox ROM from disk storage when needed. All Macs from the iMac forward are New World ROM machines, while all previous models (including all beige and platinum Macs) are Old World ROM machines.
New World ROM Macs are the first Macs where direct usage of the Open Firmware subsystem is encouraged. Previous PCI Power Macs had Open Firmware, but the implementation wasn't quite finished, since at the beginning OF was only expected to probe PCI devices, then immediately hand control over to the Mac OS ROM. Because of this, versions 1.0.5 and 2.x had several serious bugs, as well as missing functionality (such as being able to load files from an HFS partition or a TFTP server). Also, Apple set the default input and output devices to ttya (the Modem port on beige Macs), which made it difficult for normal users to get to Open Firmware; you either had to hook up a terminal, or change the settings from inside MacOS using a tool such as Boot Variables or Apple's System Disk.
The New World ROM introduced a much-improved version of the OF interpreter, version 3.0, which added many missing features, fixed most of the bugs from earlier versions, and had the capability to run CHRP boot scripts. The Toolbox ROM was embedded inside a CHRP script in the System Folder called "Mac OS ROM", along with a short loader stub and a copy of the Happy Mac icon suitable for display from Open Firmware. Once the ROM was loaded from disk, the Mac boot sequence continued as usual. As before, Open Firmware could also run a binary boot loader, and version 3.0 added support for ELF objects as well as the XCOFF files versions 1.0.5 and 2.0 supported. Also, version 3.0 (as well as some of the last releases of version 2.x, starting with the PowerBook 3400) officially supported direct access to the Open Firmware command prompt from the console (by setting the auto-boot? variable to false from MacOS, or by holding down Command-Option-O-F at boot).
One major difference between Old World ROM Macs and New World ROM Macs, at least in classic Mac OS, is that the Gestalt selector for the machine type is no longer usable; all New World ROM Macs use the same mach ID, 406 decimal, and the actual machine ID is encoded in the "model" and "compatible" properties of the root node of the Open Firmware device tree. New World ROM also sets the "compatible" property of the root node to "MacRISC2" (machines that can boot classic Mac OS using "Mac OS ROM") or "MacRISC3" (machines that can only boot Mac OS X or another Unix-like system).
External links
- The Mac ROM Enters a New World (http://developer.apple.com/technotes/tn/tn1167.html) Apple's original New World ROM documentation