BootX is a

software Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work. At the lowest programming level, executable code consists o ...

-based

bootloader A bootloader, also spelled as boot loader or called boot manager and bootstrap loader, is a computer program that is responsible for booting a computer. When a computer is turned off, its softwareincluding operating systems, application code, a ...

designed and developed by

Apple Inc. Apple Inc. is an American multinational technology company headquartered in Cupertino, California, United States. Apple is the largest technology company by revenue (totaling in 2021) and, as of June 2022, is the world's biggest company b ...

for use on the company's

Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and software en ...

computer range. BootX is used to prepare the computer for use, by loading all required

device driver In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabling operating systems and ...

s and then starting-up

Mac OS X macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac (computer), Mac computers. Within the market of ...

by booting the

kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learni ...

on all

PowerPC PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple– IBM� ...

Macintoshes running the Mac OS X 10.2 operating system or later versions. Using BootROM, a

read-only memory Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be electronically modified after the manufacture of the memory device. Read-only memory is useful for storing soft ...

(ROM)

computer chip An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny M ...

containing OpenFirmware, a graphical

bootsplash A bootsplash, also known as a bootscreen, is a graphical representation of the boot process of the operating system. A bootsplash can be a simple visualization of the scrolling boot messages in the console, but it can also present graphics or s ...

is shown briefly on all compatible Macintosh computers as a grey

Apple logo Apple Inc. is an American multinational technology company headquartered in Cupertino, California, United States. Apple is the largest technology company by revenue (totaling in 2021) and, as of June 2022, is the world's biggest company b ...

with a spinning cursor that appears during the

startup A startup or start-up is a company or project undertaken by an entrepreneur to seek, develop, and validate a scalable business model. While entrepreneurship refers to all new businesses, including self-employment and businesses that never intend t ...

sequence. The program is freely available as part of the Darwin

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

under the

open-source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized sof ...

Apple Public Source License The Apple Public Source License (APSL) is the open-source and free software license under which Apple's Darwin operating system was released in 2000. A free and open-source software license was voluntarily adopted to further involve the communit ...

. BootX was superseded by another nearly identical bootloader named boot.efi and an

Extensible Firmware Interface UEFI (Unified Extensible Firmware Interface) is a set of specifications written by the UEFI Forum. They define the architecture of the platform firmware used for booting and its interface for interaction with the operating system. Examples of f ...

ROM Rom, or ROM may refer to: Biomechanics and medicine * Risk of mortality, a medical classification to estimate the likelihood of death for a patient * Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac * R ...

on the release of the Intel-based Mac.

History

Older Macintoshes dating from 1983 until 1998 utilized a basic

; the bootloader was solely a ROM

chip Chromatin immunoprecipitation (ChIP) is a type of immunoprecipitation experimental technique used to investigate the interaction between proteins and DNA in the cell. It aims to determine whether specific proteins are associated with specific geno ...

varying in sizes up to 4

megabyte The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB. The unit prefix ''mega'' is a multiplier of (106) in the International System of Units (SI). Therefore, one megabyte is one million bytes o ...

s (MB), which contained both the

computer code A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These progra ...

to boot the computer and to run the Mac OS operating system. The ROM-resident portion of the Mac OS is the

Macintosh Toolbox The Macintosh Toolbox implements many of the high-level features of the Classic Mac OS, including a set of application programming interfaces for software development on the platform. The Toolbox consists of a number of "managers," software compone ...

and the boot-ROM part of that ROM was retroactively named Old World ROM upon the release of the New World ROM Macs, starting with the first iMac. The ROM-resident

differs greatly from the design of the modern Macintosh, which generally use a

hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magneti ...

of large capacity to store the operating system. This bootloader was used in all Macintosh computers until mid-1998. With the advent of the

iMac iMac is a family of all-in-one Mac desktop computers designed and built by Apple Inc. It has been the primary part of Apple's consumer desktop offerings since its debut in August 1998, and has evolved through seven distinct forms. In its o ...

series of Macintoshes, the firmware was updated. The ROM was reduced in size to 1 MB, called BootROM, and the remainder of the ROM was moved to the file Mac OS ROM in the Mac OS System Folder, stored on the

. This ROM used a full implementation of the OpenFirmware standard (contained in BootROM) and was named the

New World ROM New World ROM computers are Macintosh models that do not use a Macintosh Toolbox ROM on the logic board. Due to Mac OS X not requiring the availability of the Toolbox, this allowed ROM sizes to shrink dramatically (typically from to ), and facilit ...

. In 2001, with the release of

Mac OS X 10.0 Mac OS X 10.0 (code named Cheetah) is the first major release of Mac OS X, Apple's desktop and server operating system. It was released on March 24, 2001 for a price of $129 after a public beta. Mac OS X was Apple's long-awaited successor to ...

, the Mac OS ROM file was replaced with the BootX bootloader file. In 2002, with the release of Mac OS X 10.2, the historical "

Happy Mac The classic Macintosh startup sequence includes hardware tests which may trigger the startup chime, Happy Mac, Sad Mac, and Chimes of Death. On Macintosh, Macs running macOS Big Sur or later the startup sound is enabled by default, but can be di ...

" start-up picture was replaced with a grey apple logo. By introducing the Intel Mac in 2006, BootROM was replaced by the near identical

ROM (although Apple still calls it BootROM) and the boot.efi file.

Features

To make the boot loader appealing to other operating system developers, Apple added features to allow flexibility in the booting process such as

network boot Network booting, shortened netboot, is the process of booting a computer from a network rather than a local drive. This method of booting can be used by routers, diskless workstations and centrally managed computers (thin clients) such as public ...

using

TFTP Trivial File Transfer Protocol (TFTP) is a simple lockstep File Transfer Protocol which allows a client to get a file from or put a file onto a remote host. One of its primary uses is in the early stages of nodes booting from a local area network. ...

and load

Mach-O Mach-O, short for Mach object file format, is a file format for executables, object code, shared libraries, dynamically-loaded code, and core dumps. It was developed to replace the a.out format. Mach-O is used by some systems based on the Mac ...

and

ELF An elf () is a type of humanoid supernatural being in Germanic mythology and folklore. Elves appear especially in North Germanic mythology. They are subsequently mentioned in Snorri Sturluson's Icelandic Prose Edda. He distinguishes ...

formatted kernels. BootX can also boot from

HFS HFS may refer to: Computing * Hardware functionality scan, a security mechanism used in Microsoft Windows operating systems * Hierarchical File System, a file system used by Apple Macintosh computers * Hierarchical File System (IBM MVS), used ...

HFS+ HFS Plus or HFS+ (also known as Mac OS Extended or HFS Extended) is a journaling file system developed by Apple Inc. It replaced the Hierarchical File System (HFS) as the primary file system of Apple computers with the 1998 release of Mac OS 8. ...

, UFS and

ext2 The ext2 or second extended file system is a file system for the Linux kernel. It was initially designed by French software developer Rémy Card as a replacement for the extended file system (ext). Having been designed according to the same pr ...

formatted volumes. The boot loader can be manipulated at startup by holding down various key combinations to alter the booting process. Such functions include Verbose Mode, achieved by holding down the

Command Command may refer to: Computing * Command (computing), a statement in a computer language * COMMAND.COM, the default operating system shell and command-line interpreter for DOS * Command key, a modifier key on Apple Macintosh computer keyboards * ...

and V key at startup, which replaces the default

with text-based information on the boot process and Single User Mode, achieved by holding down the

and S, which, depending on the operating system, may boot into a more basic

command-line A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...

or text-based version of the operating system, to facilitate maintenance and recovery action. The ROM can also be set to require a password to access these technical functions using the OpenFirmware interface.

Boot process

In PowerPC-based Macintoshes, the

boot process In computing, booting is the process of starting a computer as initiated via Computer hardware, hardware such as a button or by a software command. After it is switched on, a computer's central processing unit (CPU) has no software in its ma ...

starts with the activation of BootROM, the basic Macintosh ROM, which performs a

Power On Self Test A power-on self-test (POST) is a process performed by firmware or software routines immediately after a computer or other digital electronic device is powered on. This article mainly deals with POSTs on personal computers, but many other embed ...

to test hardware essential to startup. On the passing of this test, the startup chime is played and control of the computer is passed to OpenFirmware. OpenFirmware initializes the Random Access Memory,

Memory Management Unit A memory management unit (MMU), sometimes called paged memory management unit (PMMU), is a computer hardware unit having all memory references passed through itself, primarily performing the translation of virtual memory addresses to physical a ...

and hardware necessary for the ROM's operation. The OpenFirmware then checks settings, stored in

NVRAM Non-volatile random-access memory (NVRAM) is random-access memory that retains data without applied power. This is in contrast to dynamic random-access memory (DRAM) and static random-access memory (SRAM), which both maintain data only for as lon ...

, and builds a list of all devices on a device tree by gathering their stored FCode information. On the completion of this task, BootX takes over the startup process configuring the keyboard and display, claiming and reserving memory for various purposes and checking to see if various key combinations are being pressed. After this process has been completed BootX displays the grey Apple logo, spins the spinning wait cursor, and proceeds to load the kernel and some kernel extensions and start the kernel.

References

External links

Mac OS X
at osxbook.com {{good article MacOS Boot loaders