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Standard PC BIOS is limited to a 16-bit processor mode and 1 MB of addressable memory space, resulting from the design based on the IBM 5150 that used a 16-bit Intel 8088 processor. [8] [34] In comparison, the processor mode in a UEFI environment can be either 32-bit (IA-32, AArch32) or 64-bit (x86-64, Itanium, and AArch64).
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). [1] The UEFI specification requires MBR partition tables to be fully supported ...
Unified Extensible Firmware Interface (UEFI) is a successor to the legacy PC BIOS, aiming to address its technical limitations. [5] UEFI firmware may include legacy BIOS compatibility to maintain compatibility with operating systems and option cards that do not support UEFI native operation.
An option ROM for the PC platform (i.e. the IBM PC and derived successor computer systems) is a piece of firmware that resides in ROM on an expansion card (or stored along with the main system BIOS), which gets executed to initialize the device and (optionally) add support for the device to the BIOS.
BIOS interrupt calls perform hardware control or I/O functions requested by a program, return system information to the program, or do both. A key element of the purpose of BIOS calls is abstraction - the BIOS calls perform generally defined functions, and the specific details of how those functions are executed on the particular hardware of the system are encapsulated in the BIOS and hidden ...
Such systems instead can drop into Real mode to switch the video mode, then draw to the framebuffer directly. In EFI 1.x systems, the INT 10H and the VESA BIOS Extensions (VBE) are replaced by the EFI UGA protocol. In widely used UEFI 2.x systems, the INT 10H and the VBE are replaced by the UEFI GOP. [1] [2]
In the context of GPT on a BIOS-based computer, a BIOS boot partition is similar in some respects to the EFI system partition, which is used by systems based on EFI. The EFI System partition holds a filesystem and files used by the UEFI, while the BIOS boot partition is used in BIOS-based systems and accessed without a filesystem by holding raw ...
Despite Microsoft's radically different definition (see below), System Information, a utility app included in Windows NT family of operating systems, refers to it as "boot device". [2] [3] The system partition is the disk partition that contains the operating system folder, known as the system root.