Now the Windows 8 64-bit operating system adopts the UEFI boot method in an all-round way. What is the difference with the Legacy boot in the past? Let us understand it together today.
How does Legacy BIOS UEFI Boot start or boot
When the system boots for the first time, Or when the system is reset, the processor will execute a code at a known location. This position is in the basic input/output system (BIOS). The CPU will call this reset vector to start a program at a known address in the flash memory/ROM. Usually, it performs a startup self-test (POST) to check the machine. Finally, it loads the first sector from the master boot record (MBR) on the boot drive.
The boot program is located in the first sector of the MBR. At this time, the boot program is loaded into RAM and executed. This boot loader is smaller than 512 bytes (a sector) in size. After the BIOS self-inspection is completed, the MBR code is read into the memory, and the management authority is handed over to the MBR. MBR reads the DPT again. From the DPT (Disk Partition Table, the hard disk partition table occupies 64 bytes of the MBR sector (offset 01BEH- -Offset 01FDH)) Find out which partition of the hard disk is the active primary partition. So far, so the system is the same. There is a difference below. After DPT reads and finds the primary partition, it finds the PBR (Partition Boot Record) of this primary partition. The PBR is located in the first sector of the active primary partition. PBR will be changed when different operating systems are installed. The dead code of PBR in XP is to find NTLDR. And what is written in the PBR of Vista and 7 is to find Bootmgr.
At this time, there is no boot manager interface displayed on the monitor. After Bootmgr was found, the management rights were handed over to Bootmgr. Boot Manager first reads the language version information of the Boot Manager menu from the BCD, and then calls BOOTMGR and BOOTMGR.EXE.MUI in the corresponding language to form the boot menu of the corresponding language, and then the boot manager is displayed on the display, that is, select That text interface for multiple operating systems. Finally, when you select the corresponding operating system, here is Win7 or 8 (if you select XP, it will go to the XP boot process, find XP’s NTLDR and then start), Bootmgr will look for the system partition (the system partition and the main partition) The concept is not the same) Winload.exe under Windows/System32 loads the operating system kernel.
EFI Boot Introduction
EFI stands for Extensible Firmware Interface (Extensible Firmware Interface), which is Intel’s brand new type of firmware architecture and interface And the recommended standards proposed by the service. The standard has two main purposes: to provide a standard operating environment for the boot program of the operating system and certain applications that run when the computer is initialized; and to provide an interactive protocol for the operating system to communicate with the firmware.
In short, EFI is a replacement for BIOS. It provides a more powerful, safer and more convenient way to interact with the operating system and firmware. The interface defined by the EFI specification, including the data table contains platform information, can be used in the OS Loader and OS startup and runtime services.
EFI firmware provides several technical advantages:
- < p>The boot capability supports large-capacity disks (more than 2 TIB);
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Faster startup;
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Independent CPU Architecture;
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CPU independent driver;
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Flexible pre-operating system environment, including network functions;
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Modular design;
EFI startup also requires a special partition table, which points to a special file. Normally, the file is located in the EFI path. EFI startup involves a boot loader that is written to the firmware. EFI does not place the boot program in the MBR. The firmware knows how to read the partition table and the FAT file format. The EFI system partition is a specific partition formatted in FAT format, which contains the boot loader, which is an EFI executable program that can be loaded and run by the EFI boot manager.
Boot loader is set as a file that can be accessed through firmware. Boot loader allows users to select and load the operating system. All boot managers contain an EFI variable, which is used to define firmware configuration parameters.
MBR and GPT
MBR: Master Boot Record (Master Boot Record, abbreviation: MBR), also known as the master boot sector, is the location when the computer accesses the hard disk after the computer is turned on. The first sector that must be read, its three-dimensional address on the hard disk is (cylinder, head, sector) = (0, 0, 1).
The master boot sector records the relevant information of the hard disk itself and the size and location information of each partition of the hard disk. It is an important entry for data information. If it is damaged, the basic data structure information on the hard disk will be lost, and the original data can be accessed only after tentatively reconstructing the data structure information in a tedious way. The information in the master boot sector is written through the partition program. It is a product of low-level formatting and has nothing to do with the operating system (the operating system is created on a high-level formatted hard disk partition, and is related to a certain file system. Related).
For hard disks, the possible number of bytes in a sector is 128×2n (n=0,1,2,3) . In most cases, n=2, that is, the size of a sector is 512 bytes.
MBR restrictions:
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In the MBR partition table, there are at most 4 primary partitions or 3 primary partitions + 1 extended partition: From the structure of the master boot record, it can be known that it only contains a 64-byte hard disk partition table. Since each partition information requires 16 bytes, for a hard disk with an MBR partition structure, only 4 primary partitions (Primary partition) can be identified at most.
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MBR partition scheme cannot support disks with a capacity exceeding 2TB. Because this scheme uses 4 bytes to store the total number of sectors in a partition, the maximum number of sectors to the 32th power of 2 can be expressed. The maximum number of sectors is 512 bytes per sector, and the maximum number of each partition cannot exceed 2TB. After the disk capacity exceeds 2TB, the starting position of the partition can no longer be expressed.
GPT: Globally unique identification partition table (GUID Partition Table, abbreviation: GPT) is an entity The partition structure of the hard disk. GUID Partition Table (GPT) was introduced as part of the Extensible Firmware Interface (EFI) plan. Compared with the older master boot record (MBR) partitioning scheme commonly used by PCs, GPT provides a more flexible disk partitioning mechanism.
GPT uses GUID partition table (GPT) disk partition system. GPT disks provide the following benefits:
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allows up to 128 partitions; master boot record (MBR ) The disk can support 124 additional partitions in 4 primary partitions and extended partitions.
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Volume capacity larger than 2TB is allowed, and 2TB is the limit of MBR disk.
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Because the partition table provides replication and cyclic redundancy check (CRC) protection, So it is more reliable.
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Can be used as a storage volume on all x64-based platforms, including running Windows XP Professional x64 Edition platform. Starting from Windows Server 2003 SP1, GPT disks can also be used as storage volumes on the x86-based Windows platform.
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Can be used on x64-based Windows 7, Windows Vista and Windows Server 2008 versions Boot volume. Starting from Windows Server 2003 SP1, GPT disks can also be used as boot volumes on Itanium-based systems.
Note: Windows only supports booting firmware from systems that include Unified Extensible Firmware Interface (UEFI) The GPT disk boot.
The difference between GOP and VBIOS
VBIOS is the BIOS of a computer graphics card or integrated graphics controller, similar to a system BIOS provides a set of program functions used by software to access Like the system hardware, VBIOS also provides a set of functions used by video-related programs to access the video hardware. Usually, the graphics card manufacturer provides a binary Bin file to the ODM manufacturer and wraps it in the system BIOS.
And GOP (Graphic Output Protocol) driver is the EFI driver that replaces the traditional VBIOS black box under the EFI architecture. It is designed to be booted in the operating system The graphic output function that supports the basic needs before.
VBT: Video bios table. VBT is a special binary data block specially made for customization. Rely on BMP utility to edit. VBT also records display parameter information such as detail timing, GPIO Pins, and Clock just like legacy vbios.
The difference between the two: During the Pre-OS boot period, EFI uses the standard GOP protocol to achieve display and output. And lagacy vbios needs to be achieved through INT10 interrupter.
Which systems support UEFI boot ? Why can’t we currently support 32bit win8 UEFI boot?
Currently our BIOS The Build is in x64 mode, so the 32-bit Win8 UEFI is not supported.