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iBoot
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<p>iBoot is the stage 2 <a href="/facts/Bootloader/6sNpcLMK">bootloader</a> for <a href="/facts/IPhone/h5WeKRl9">iPhones</a>, <a href="/facts/IPad/Ql67x0Dw">iPads</a>, <a href="/facts/Apple_silicon/A8RgouDB">Apple silicon</a>-based Macs, and the <a href="/facts/Apple_T2/A8RgouDB">T2 chip</a> in Intel-based <a href="/facts/Mac_(computer)/8GhnXTK0">Macs</a> with such a chip. Compared with its predecessor, iBoot improves authentication performed in the boot chain. </p><p>For Intel-based Macs with a T2 chip, the boot process starts by running code on the T2 chip from the <a href="/facts/Boot_ROM/j6N1kRpc">boot ROM</a>. That <a href="/facts/Boot_ROM/j6N1kRpc">boot ROM</a> loads and runs iBoot onto the T2 chip; iBoot loads the <a href="/facts/BridgeOS/SXLPoBB1">bridgeOS</a> operating system onto the T2 chip and starts it; bridgeOS loads the <a href="/facts/UEFI/w86VGmy2">UEFI</a> firmware; UEFI firmware starts the main Intel processor and completes the <a href="/facts/Power-On_Self_Test/zwTA1bhH">Power-On Self Test</a> process. The UEFI firmware loads boot.efi, which loads and starts the macOS kernel. </p><p>For iPhones, iPads and Apple silicon-based Macs, the boot process starts by running the device's boot ROM. On iPhones and iPads with <a href="/facts/Apple_A9/0fvStBD5">A9</a> or earlier A-series processors, the boot ROM loads the Low-Level Bootloader (LLB), which is the stage 1 bootloader and loads iBoot; on Macs and devices with A10 or later processors, the boot ROM loads iBoot. If all goes well, iBoot will then proceed to load the <a href="/facts/IOS/mK5cggH5">iOS</a>, <a href="/facts/IPadOS/fClrmH7D">iPadOS</a> or <a href="/facts/MacOS/Y93vVpTm">macOS</a> kernel as well as the rest of the operating system. If iBoot fails to load or fails to verify iOS, iPadOS or macOS, the bootloader jumps to DFU (Device Firmware Update) mode; otherwise it loads the remaining <a href="/facts/Kernel_(operating_system)/uEj4U3Rz">kernel</a> modules. </p><p>Once the kernel and all drivers necessary for booting are loaded, the boot loader starts the kernel’s initialization procedure. At this point, enough drivers are loaded for the kernel to find the root device. </p><p>Since <a href="/facts/Apple_A7/WIaQPsQe">Apple A7</a>, the LLB and iBoot are stored on NAND flash of iPhone or iPad; since <a href="/facts/Apple_M1/vaTA4u2J">Apple M1</a>, the LLB is stored on the internal SSD of Apple silicon Mac. </p>