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Target Disk Mode (sometimes referred to as TDM or Target Mode) is a boot mode unique to Macintosh computers. When a Mac that supports Target Disk Mode [1] is started with the 'T' key held down, its operating system does not boot. Instead, the Mac's firmware enables its drives to behave as a SCSI, FireWire, Thunderbolt, or USB-C external mass ...
The first memory location the CPU tries to execute is known as the reset vector. In the case of a hard reboot, the northbridge will direct a code fetch request to the BIOS located on the system flash memory. For a warm boot, the BIOS will be located in the proper place in RAM and the northbridge will direct the reset vector call to the RAM. In ...
Macs made from 1984 to 1998 used Old World ROM as the boot loader for all Macs produced around that time period. From 1998 up until the PowerPC to Intel transition, New World ROM was used for all Macs starting with the first iMac and later expanding to the first iBook and the Blue and White Power Mac G3.
The conventional MBR code checks the MBR's partition table for a partition set as bootable [nb 6] (the one with active flag set). If an active partition is found, the MBR code loads the boot sector code from that partition, known as Volume Boot Record (VBR), and executes it. The MBR boot code is often operating-system specific.
For example, in the x86 architecture, asserting the RESET line halts the CPU; this is done after the system is switched on and before the power supply has asserted "power good" to indicate that it is ready to supply stable voltages at sufficient power levels. [2] Reset places less stress on the hardware than power cycling, as the power is not ...
macOS Monterey is the final version of macOS that supports the 2015–2017 MacBook Air, Retina MacBook Pro, 2014 Mac Mini, 2015 iMac and cylindrical Mac Pro, as its successor, macOS Ventura, drops support for those models. It is the last version of macOS that can run on Macs with 4GB of RAM.
Those Macintoshes include a ROM chip varying in sizes up to 4 megabytes (MB), [8] which contains both the computer code to boot the computer and to run the Mac OS operating system. The ROM-resident portion of the Mac OS is the Macintosh Toolbox and the boot-ROM part of that ROM was retroactively named Old World ROM upon the release of the New ...
The boot ROM is mapped into memory at a fixed location, and the processor is designed to start executing from this location after reset, according to the processor's reset vector. The boot ROM is either placed on the same die as the CPU or is an external ROM chip.