startup disk in the parameter RAM. If a bootable disk is found, the Happy Mac logo is displayed, and control is handed over to the Mac OS. If no disk to boot from is present, an icon depicting a floppy disk with a blinking question mark in the middle will be displayed. If a hardware problem occurs during the early part of the boot process, the machine will display the Sad Mac icon with a hexadecimal error code and freeze; on Macs made after 1987, this will be accompanied by the Chimes of Death sound. Since the Old World ROM usually boots to Toolbox, most OSs have to be installed using a boot loader from inside Mac OS (BootX is commonly used for Linux installations). 68K-based Macs and NuBus Power Macs must have Mac OS installed to load another OS (even A/UX, which was an Apple product), usually with virtual memory turned off. PCI Power Macs can be configured to boot into Open Firmware, allowing the firmware to load a boot loader directly, or they can use a specially-prepared floppy disk to trick the Toolbox into loading a kernel (this is used for Linux installation floppy images). The simplest way to identify an Old World ROM Mac is that it will not have a factory built-in USB port. Only New World ROM Macs featured a USB port as factory equipment. See also BootX (Linux), the standard LinuxPPC boot loader for Old World machines Quik (boot loader), a replacement boot loader for Old World PCI systems External links Macintosh operating systems Macintosh firmware