Use in booting Because much of the Toolbox is implemented in ROM, alongside the computer's firmware, it was convenient to use as a bootloader environment. In conjunction with resources stored on the ROM chip, the Toolbox can turn the screen gray, show a dialog box with the signature "Welcome to Macintosh" greeting, and display the mouse cursor. By using Toolbox to help boot the machine, a rudimentary Mac-like environment can be initialized before ever loading the System suitcase from disk (in fact before ROMs on NuBus cards were executed), which is when the decision to use 24-bit or 32-bit addressing has to be made. (System 7's support for 32-bit addressing requires 32-bit clean ROMs, as older Mac ROMs do not have support for this). The need for diagnostics as in the BIOS resident for IBM PC compatibles' boards is not necessary since the Macintosh has most of its diagnostics in POST and automatically reports errors via the "Sad Mac" codes. The similarity between the boot-up environment and the actual operating system should not be confused with being identical, however. Although the "Classic Mac OS" boot process is convoluted and largely undocumented, it is not more limited than an IBM PC compatible BIOS. Like a PC's master boot record, a ROM-based Mac reads and executes code from the first blocks ("boot blocks") of the disk partition selected as the boot device. The boot blocks then verify that a suitable rudimentary environment exists, and use it to load the System suitcase. A different operating system with a different file system can boot by simply using its own code in the boot blocks. This system was not used for PowerPC Linux, however, because Open Firmware in New World ROM machines requires a bootloader within an HFS filesystem—a reason having nothing to do with the Toolbox or "old-fashioned" Macs in general. More narrowly, the Startup Disk control panel in the Classic Mac OS and macOS only allows the user to select a mounted filesystem with very particular constraints. Legacy In Mac OS X, the Toolbox is not used at all, though the Classic Environment loads the Toolbox ROM file into its virtual machine. Much of the Toolbox was restructured and implemented as part of Apple's Carbon programming API, allowing programmers familiar with the Toolbox to port their program code more easily to Mac OS X. See also Mac OS memory management References External links