Misplaced Pages

#376623

36-413: An ESP contains the boot loaders , boot managers , or kernel images of installed operating systems (which are typically contained in other partitions), device driver files for hardware devices present in a computer and used by the firmware at boot time, system utility programs that are intended to be run before an operating system is booted, and data files such as error logs. The EFI system partition

72-542: A basic execution environment , and locates the second-stage bootloader. Its primary challenge lies in accomplishing these tasks within strict size constraints while handling potential hardware failures. The bootloader must navigate disk structures, often implementing FAT file system support, and manage the delicate transition from the BIOS startup state to a stable environment for the next boot stage. Boot loaders may face peculiar constraints, especially in size; for instance, on

108-631: A basic shell (as in GNU GRUB), or even games (see List of PC booter games ). Some boot loaders can also load other boot loaders; for example, GRUB loads BOOTMGR instead of loading Windows directly. Usually, a default choice is preselected with a time delay during which a user can press a key to change the choice; after this delay, the default choice is automatically run so normal booting can occur without interaction. They may also handle compression, cryptographic verification, and chain-loading of other bootloaders. The boot process can be considered complete when

144-523: A boot loader needs to be stored according to the standard ESP file hierarchy, or by providing a complete path of a boot loader to the system's boot manager. On the other hand, FAT32 is always expected on fixed drives. GRUB 2 , elilo and systemd-boot serve as conventional, full-fledged standalone UEFI boot managers (a.k.a. bootloader managers) for Linux. Once loaded by a UEFI firmware, they can access and boot kernel images from all devices, partitions and file systems they support, without being limited to

180-507: A boot loader reaching over two physical sectors, using 386 instructions for size reasons. At the same time, other vendors managed to squeeze much more functionality into a single boot sector without relaxing the original constraints on only minimal available memory (32 KiB) and processor support (8088/8086). For example, DR-DOS boot sectors are able to locate the boot file in the FAT12, FAT16 and FAT32 file systems, and load it into memory as

216-400: A mere process within that system, and then irrevocably transfer control to the operating system. The boot loader then terminates normally as any other process would. Most computers are also capable of booting over a computer network . In this scenario, the operating system is stored on the disk of a server , and certain parts of it are transferred to the client using a simple protocol such as

252-555: A peripheral device, may load a very small number of fixed instructions into memory at a specific location, initialize at least one CPU, and then point the CPU to the instructions and start their execution. These instructions typically start an input operation from some peripheral device (which may be switch-selectable by the operator). Other systems may send hardware commands directly to peripheral devices or I/O controllers that cause an extremely simple input operation (such as "read sector zero of

288-418: A relatively small program stored in read-only memory (ROM, and later EEPROM , NOR flash ) along with some needed data, to initialize RAM (especially on x86 systems), to access the nonvolatile device (usually block device , e.g., NAND flash) or devices from which the operating system programs and data can be loaded into RAM. Some earlier computer systems, upon receiving a boot signal from a human operator or

324-516: A single kernel image to work in any boot environment. Linux kernel's support for the EFI Boot Stub is enabled by turning on option CONFIG_EFI_STUB (EFI stub support) during the kernel configuration. It was merged into version 3.3 of the Linux kernel mainline , released on March 18, 2012. Systemd-boot is a simple UEFI boot manager that loads and runs configured EFI images, accessing only

360-422: A small program from a special section (most commonly the boot sector ) of the most promising device, typically starting at a fixed entry point such as the start of the sector. A first-stage bootloader is a compact 512-byte program that resides in the master boot record (MBR) and executes when a computer starts. Running in 16-bit real mode at address 0x7C00, it performs minimal hardware initialization , sets up

396-430: A whole via CHS or LBA, even if the file is not stored in a fixed location and in consecutive sectors. BIOS and UEFI can not only load multiple operating systems from a non-volatile device, they can also initialize system hardware for the loaded operating systems. Examples of first-stage bootloaders include BIOS , UEFI , coreboot , Libreboot , and Das U-Boot . Second-stage bootloaders operate without

SECTION 10

#1732791856377

432-492: Is a computer program that is responsible for booting a computer. If it also provides an interactive menu with multiple boot choices then it's often called a boot manager . When a computer is turned off, its software‍—‌including operating systems, application code, and data‍—‌remains stored on non-volatile memory . When the computer is powered on, it typically does not have an operating system or its loader in random-access memory (RAM). The computer first executes

468-438: Is booted. EFI Boot Stub makes it possible to boot a Linux kernel image without the use of a conventional UEFI boot loader. By masquerading as a PE / COFF executable image and appearing to the firmware as a UEFI application, a Linux kernel image with EFI Boot Stub enabled can be directly loaded and executed by a UEFI firmware. Such kernel images can still be loaded and run by BIOS-based boot loaders; thus, EFI Boot Stub allows

504-540: Is formatted with a file system whose specification is based on the FAT file system and maintained as part of the UEFI specification; therefore, the file system specification is independent from the original FAT specification. The actual extent of divergence is unknown: Apple maintains a separate tool that should be used on Intel/x86-64 Macs, while other systems use FAT utilities just fine. The globally unique identifier (GUID) for

540-459: Is located at the \EFI\Microsoft\Boot\ subfolder of the EFI system partition. On Windows XP 64-Bit Edition and later, access to the EFI system partition is obtained by running the mountvol command. Mounts the EFI system partition on the specified drive. Available on Itanium-based computers only. Boot loader A bootloader , also spelled as boot loader or called bootstrap loader ,

576-458: Is necessary, because the loading can be precomputed and stored on the ROM when the device is made. Large and complex systems may have boot procedures that proceed in multiple phases until finally the operating system and other programs are loaded and ready to execute. Because operating systems are designed as if they never start or stop, a boot loader might load the operating system, configure itself as

612-487: The Trivial File Transfer Protocol (TFTP). After these parts have been transferred, the operating system takes over the control of the booting process. As with the second-stage boot loader, network booting begins by using generic network access methods provided by the network interface's boot ROM, which typically contains a Preboot Execution Environment (PXE) image. No drivers are required, but

648-464: The extended BIOS parameter block on FAT12 and FAT16 volumes since DOS 4.0, whereas the FAT32 EBPB introduced with DOS 7.1 requires even 87 bytes, leaving only 423 bytes for the boot loader when assuming a sector size of 512 bytes. Microsoft boot sectors, therefore, traditionally imposed certain restrictions on the boot process. For example, the boot file had to be located at a fixed position in

684-530: The kernel . Many implement modular designs supporting loadable modules for additional functionality. These choices can include different operating systems (for dual or multi-booting from different partitions or drives), different versions of the same operating system (in case a new version has unexpected problems), different operating system loading options (e.g., booting into a rescue or safe mode ), and some standalone programs that can function without an operating system, such as memory testers (e.g., memtest86+ ),

720-589: The master boot record in order to leave room for the default 64-byte partition table with four partition entries and the two-byte boot signature , which the BIOS requires for a proper boot loader — or even less, when additional features like more than four partition entries (up to 16 with 16 bytes each), a disk signature (6 bytes), a disk timestamp (6 bytes), an Advanced Active Partition (18 bytes) or special multi-boot loaders have to be supported as well in some environments. In floppy and superfloppy volume boot records , up to 59 bytes are occupied for

756-472: The BIOS-based CSM booting upon detecting certain types of partition table on the boot disk, effectively preventing UEFI booting from being performed from EFI system partitions contained on MBR-partitioned disks. UEFI firmware supports booting from removable storage devices such as USB flash drives . For that purpose, a removable device is formatted with a FAT12 , FAT16 or FAT32 file system, while

SECTION 20

#1732791856377

792-554: The EFI system partition in the GUID Partition Table (GPT) scheme is C12A7328-F81F-11D2-BA4B-00A0C93EC93B , while its ID in the master boot record (MBR) partition-table scheme is 0xEF . Both GPT- and MBR-partitioned disks can contain an EFI system partition, as UEFI firmware is required to support both partitioning schemes. Also, El Torito bootable format for CD-ROMs and DVDs is supported. UEFI provides backward compatibility with legacy systems by reserving

828-478: The EFI system partition is initially left blank and unused for booting into macOS . However, the EFI system partition is used as a staging area for firmware updates and for the Microsoft Windows bootloader for Mac computers configured to boot into a Windows partition using Boot Camp . Custom Apple UEFI firmware named iBoot controls the logic for finding and loading bootloaders. iBoot will select

864-417: The EFI system partition. The mount point for the EFI system partition varies depending on the bootloader used. Older bootloaders such as GRUB 2 and lilo/elilo default to /boot/efi . Alternatively, systemd-boot prefers either /efi or /boot over /boot/efi due to potential complications with nested autofs mounts. Regardless of the mount point path, its contents are accessible after Linux

900-418: The EFI system partition. Configuration file fragments, kernel images and initrd images are required to reside on the EFI system partition, as systemd-boot does not provide support for accessing files on other partitions or file systems. Linux kernels need to be built with CONFIG_EFI_STUB=y so they can be directly executed as UEFI images. On Apple Mac computers using Intel x86-64 processor architecture,

936-509: The bootstrapping process begins with the CPU executing software contained in ROM (for example, the BIOS of an IBM PC or an IBM PC compatible ) at a predefined address (some CPUs, including the Intel x86 series , are designed to execute this software after reset without outside help). This software contains rudimentary functionality to search for devices eligible to participate in booting, and load

972-450: The computer is ready to interact with the user, or the operating system is capable of running system programs or application programs. Many embedded systems must boot immediately. For example, waiting a minute for a digital television or a GPS navigation device to start is generally unacceptable. Therefore, such devices have software systems in ROM or flash memory so the device can begin functioning immediately; little or no loading

1008-470: The desired bootloader (potentially configured via Startup Keyboard Combinations or NVRAM ), optionally falling back to either the internal macOS Installation, or a recovery system called recoveryOS . Older pre-UEFI Apple–Intel architecture machines required the EFI system partition to be formatted in HFS+ . Third-party bootloaders needed to be "blessed" by a special ioctl command before becoming bootable by

1044-406: The earlier IBM PC and compatibles, a boot sector should typically work with 510 bytes of code (or less) and in only 32 KiB (later relaxed to 64 KiB ) of system memory and only use instructions supported by the original 8088 / 8086 processors. The first stage of PC boot loaders (FSBL, first-stage boot loader) located on fixed disks and removable drives must fit into the first 446 bytes of

1080-663: The firmware, a relic of the System Folder blessing from Classic Mac OS . There are otherwise no limitations to what kinds of EFI operating system or bootloader an Intel-based Apple computer can run. Devices using Apple silicon ( AArch64 ) such as iPhones, iPads and all Mac computers from 2023 onward do not contain EFI/UEFI functionality and subsequently do not use EFI system partitions. UEFI support in Windows began in 2008 with Windows Vista SP1. The Windows boot manager

1116-648: The first block (sector) of the partition for compatibility code, effectively creating a legacy boot sector . On legacy BIOS -based systems, the first sector of a partition is loaded into memory, and execution is transferred to this code. UEFI firmware does not execute the code in the MBR, except when booting in legacy BIOS mode through the Compatibility Support Module (CSM). The UEFI specification requires MBR partition tables to be fully supported. However, some UEFI implementations immediately switch to

EFI system partition - Misplaced Pages Continue

1152-601: The operating system subsequently initializes itself and may load extra device drivers . The second-stage boot loader does not need drivers for its own operation, but may instead use generic storage access methods provided by system firmware such as the BIOS or Open Firmware , though typically with restricted hardware functionality and lower performance. Second-stage implementations can include interactive user interfaces, allowing boot option selection and parameter modification. They handle kernel loading, including processing of initrd/initramfs images, and can pass boot parameters to

1188-480: The root directory of the file system and stored within consecutive sectors, conditions taken care of by the SYS command and slightly relaxed in later versions of DOS. The boot loader was then able to load the first three sectors of the file into memory, which happened to contain another embedded boot loader able to load the remainder of the file into memory. When Microsoft added LBA and FAT32 support, they switched to

1224-867: The strict 512-byte limitation of their first-stage counterparts. They execute in a more sophisticated environment, typically ranging from 8KB to several megabytes in size. This expanded space allows implementation of complex features including multiple filesystem support, runtime configuration, and bootloader menu interfaces. Second-stage bootloaders perform comprehensive hardware initialization. They query and configure various system components including memory controllers , interrupt controllers , and essential peripherals. Modern implementations often handle ACPI tables, USB controller initialization, and preliminary graphics setup. Second-stage boot loaders, such as GNU GRUB , rEFInd , BOOTMGR , Syslinux , NTLDR or iBoot , are not themselves operating systems, but are able to load an operating system properly and transfer execution to it;

1260-527: The system device into memory starting at location 1000") to be carried out, effectively loading a small number of boot loader instructions into memory; a completion signal from the I/O device may then be used to start execution of the instructions by the CPU. Smaller computers often use less flexible but more automatic boot loader mechanisms to ensure that the computer starts quickly and with a predetermined software configuration. In many desktop computers, for example,

1296-573: The system functionality is limited until the operating system kernel and drivers are transferred and started. As a result, once the ROM-based booting has completed it is entirely possible to network boot into an operating system that itself does not have the ability to use the network interface. Linux kernel mainline Too Many Requests If you report this error to the Wikimedia System Administrators, please include

#376623