Editing Macintosh Toolbox (section)

== Functionality ==
=== Programming interfaces ===
The Toolbox is composed of commonly used functions, but not the ''most'' commonly used functions. As a result, it grew into a hodgepodge of different API [[Library (computing)|libraries]].<ref name=macalmanac/> The Toolbox encompasses most of the basic functionality which distinguished the Classic Mac OS. Apple's references “Inside Macintosh: Macintosh Toolbox Essentials” and “Inside Macintosh: More Macintosh Toolbox”, similarly vague in scope, also document most of the Toolbox.

=== 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 [[resource (Macintosh)|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 compatible]]s' boards is not necessary since the Macintosh has most of its diagnostics in [[power-on self-test|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.<ref>{{cite web|url=https://developer.apple.com/documentation/mac/OSUtilities/OSUtilities-189.html#HEADING189-31|title=Boot Blocks|author=Apple Inc. |date=6 July 1996 |archive-url=https://web.archive.org/web/20040312135108/http://developer.apple.com/documentation/mac/OSUtilities/OSUtilities-189.html#HEADING189-31 |archive-date=2004-03-12}} [http://mirror.informatimago.com/next/developer.apple.com/documentation/mac/OSUtilities/OSUtilities-189.html#HEADING189-31 Alt URL]</ref> 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 later macOS only allows the user to select a mounted filesystem with very particular constraints.