Booting

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Booting is the process of starting a computer. For various Macintosh systems, there are very different boot processes, depending on the vintage of the system.
==Classic Mac OS==
===Old World ROM===
Starting with the original Macintosh 128K from 1984, classic Macs powered up with a beep and then loaded the Old World ROM, which contained Bill Atkinson's Macintosh Toolbox and was stored in ROM chips on the logic board, which then immediately looked for a startup disk containing the System file. Success would be indicated by a Happy Mac icon. The Macintosh II in 1987 and most later models replaced the startup beep with a chime. During the PowerPC transition, PCI-based Power Macintosh systems from 1995 began transitioning to an Open Firmware (OF) implementation of the Old World ROM.
===New World ROM===
When the iMac, the "blue and white" Power Mac G3, and the bronze-keyboard PowerBook G3 were introduced in 1998 and 1999 by the newly-returned Steve Jobs, Macintosh computers began using New World ROMs, that switched from relying on the Macintosh Toolbox to only Open Firmware on the logic board. The Mac OS ROM was moved from the logic board into a file in the classic System Folder, which was a necessary step in the transition from classic Mac OS to Mac OS X.
==Mac OS X==
When power is turned on PowerPC-based systems with Mac OS X, Open Firmware (OF) code is executed. Control is then passed to the bootloader, which is located at /System/Library/CoreServices/BootX and loads the kernel. Intel-based Macs load from an Extensible Firmware Interface (EFI) ROM which looks for Boot.efi instead.What happens in the Mac OS X boot process? at OSXDaily. 2007-01-22
==macOS==
Starting in 2016, Apple removed startup chimes from all new models (except the MacBook Air) by default, but it may be re-enabled in Terminal with the following undocumented (and unsupported) command:New MacBook Pros lack iconic Mac startup chime, but they do automatically boot when you open the lid (update: here’s how to enable it) by Benjamin Mayo, 9to5Mac. 2016-10-30.
:sudo nvram BootAudio=%01
Changes to macOS by Apple caused the above option not to work on 2017 models, but users discovered another undocumented command:TipBITS: Enable the Startup Chime on New Macs by Adam Engst, TidBITS. 2020-02-24.
:sudo nvram StartupMute=%00
Starting with the iMac Pro and the 2018 MacBook Pro, bootup is controlled by Apple's new T2 chip, which also controls encryption of user data to flash-based drives.T2 chip in iMac Pro & 2018 MacBook Pro controls boot, security functions previously managed by CPU by Mike Wuerthele, AppleInsider. 2018-01-04. The bridgeOS within the T2 chip contains a deeper startup chime that is disabled by default, but can be enabled with the above command. macOS Big Sur re-enabled startup chimes by default when it was released in November 2020.New Mac Startup Chime (T2 Macs) that I got in high quality after extracting an image of the T2 Chip's BridgeOS. Enjoy! by Martin Nobel, Reddit. 2020-08-03.
==References==
==See also==
*Firmware password
==External links==
*About Mac startup tones at Apple Support
**Boot process for an Intel-based Mac (2021-02-18)
**Boot process for a Mac with Apple silicon(2021-02-18)
*Boot Beep by Andy Hertzfeld at Folklore (1982-09)
*The [Classic] Macintosh Boot Sequence at James Madison University
*A Brief History of Apple and EFI at rEFIt
*Booting at Wikipedia
**[Classic] Macintosh startup and BootX (Apple)
Category:Technical terminology