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 Mac OS, or by holding down --- 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. The 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). It is somewhat easier to boot a non-Mac-OS operating system on a New World system, and indeed OpenBSD's bootloader only works on a New World system. The simplest way to distinguish a New World ROM Mac is that it will have a factory built-in USB port. No Old World ROM Mac had a USB port as factory equipment; instead, they used ADB for keyboard and mouse, and mini-DIN-8 "modem" and "printer" serial ports for other peripherals. Also, New World ROM Macs generally do not have a built-in floppy drive. References External links The Mac ROM Enters a New World Apple's original New World ROM documentation MacOS Macintosh operating systems Macintosh firmware