computer systems

 computer systems

unmodified computers can use their BIOS as an intermediary for booting Windows operating systems, or a virtual boot loader, up to the point where the boot loader needs to transfer control to a new device, such as a virtual device (such as a Virtual Machine or a Hyper-V virtual machine) or to another OS (e.g. Linux). A boot manager only receives this type of information when a user chooses to do so.[1] For example, the BIOS may be used as a Windows loader to transfer control to a Virtual Machine, while the UEFI boot manager offers only this function for UEFI implementations, since UEFI requires a self-contained kernel to be loaded and use the boot manager as the OS loader.[2] In addition, an alternative self-contained kernel may be loaded by the boot manager instead of the Windows loader, and such a boot manager may be used to install a hypervisor.[3] In systems without a boot manager, the UEFI boot manager and an alternative self-contained kernel must be installed in the next step. Kernel-assisted loading [ edit ] The UEFI boot manager in Vista/Windows 7 provides a boot menu, the access point for enabling or disabling certain functions during the boot process, such as secure boot. The user can also configure the boot order in which the different booting mechanisms take over control from the boot manager.[4][5][6] The list of boot-supportable functions can be used to guide the user to install a suitable boot loader.[7] Extensible boot loader [ edit ] In Windows Vista and newer versions of Windows, UEFI can be used with certain Linux distributions. For instance, Fedora,[8] OpenSUSE,[9] and Debian[10] support booting from UEFI Secure Boot on supported platforms. The Extensible Boot loader (EBI) replaces the FAT and NTFS boot paths with bootable images. EBI can be used with kernels compiled with SysV init, UBIFS, and Samba. Additionally, this allows Linux distributions to boot from UEFI Secure Boot if the underlying host platform supports booting from UEFI Secure Boot.[11] If it is not possible to use UEFI Secure Boot or a later boot loader on the computer, the Secure Boot loader can be replaced with the legacy GRUB boot loader.[12] Blank BIOS [ edit ] If the motherboard manufacturer does not provide a default UEFI BIOS with specified boot options, users can set up bootloader keys for their specific system. The BIOS has a feature that allows users to disable booting from the UEFI firmware. Users can disable booting the UEFI firmware and not be forced to use an alternate boot loader. However, some users of AMD chipsets have reported that disabling the UEFI firmware by pressing one of two keys on the motherboard will disable the entire computer system.[13][14] This can be circumvented by pressing the power button, which disables the CPU and returns power to the motherboard. As this technique involves compromising the security of the computer, it should be used only with caution and with all necessary measures taken to avoid exposure to the attacker. Generation 3.x [ edit ] One example of this form of boot loader (identical to GRUB2 for most platforms) is "Live Recovery Mode". This is a bootloader and service loader developed by Intrusion Inc. for Jorn Torp. It was in the FreeBSD source tree since version 7.3 and the OpenBSD repositories since version 8.4. Other distributions of Linux often ship with Live Recovery Mode built in (for example, Ubuntu 16.04[15]). Live Recovery Mode only exists as a kernel driver which can be applied to kernels compiled for certain x86 platforms. This method offers minimal functionality and can not boot a system.[16][17] Booting from physical media [ edit ] Hardware manufacturers provide many different ways to boot a computer. When booting from a floppy disk, the computer might boot from a serial console, or from a CD-ROM drive. In many cases, computers can boot from a network, a hard drive, or another device attached to the motherboard. Devices that support live CD support booting