Two boot modes for UEFI and Legacy bios

Source: Internet
Author: User

(1), UEFI boot mode and legacy boot mode

Legacy Boot mode: That's how the PC has been using it for years (loading the launcher from the MBR), and the UEFI BIOS as a new BIOS should naturally be compatible with this old boot mode;

UEFI Boot mode: New boot technology under UEFI BIOS. If your PC is preloaded with WIN8 in UEFI boot mode, you will find two very small hidden partitions. One is called ESP (EFI System partition), another MSR (Microsoft Reserved partition, usually 128MB). The MSR is required by Windows. ESP is important for UEFI boot mode, where UEFI boot programs are stored in the ESP partition with files named. EFI, and the ESP partition uses the FAT32 file system. In addition, there may be a small partition called WinRE Tools, which is the WIN8 recovery partition and is small in size. So don't delete these three partitions.

So the first key issue is to determine your startup mode by entering the BIOS, and then you will find that there is a "boot mode", "Uefi boot" is the UEFI boot mode, check "Legacy boot" is the Legacy boot mode.

(2), UEFI boot mode only supports 64-bit system, so the pre-installed WIN8 is 64-bit, Ubuntu (Bantu) is a desktop application-oriented Linux operating system, also requires 64-bit.

(3), UEFI BIOS and Legacy bios

We all know that the boot priority of the device can be adjusted in the traditional BIOS, and the UEFI BIOS can not only adjust the priority of the device in Uefi boot mode, but also adjust the priority of the boot program in the device, after installing Ubuntu, If you go into the BIOS again, you'll find an alternative startup item called Ubuntu. In addition, the UEFI BIOS introduces some new technologies, such as fast boot and secure boot, and, of course, the latter is entirely for the pit daddy.

(4), how to boot from the U disk or the removable hard disk in Uefi boot mode

As long as there is a FAT32 partition on the U-disk or mobile hard disk, a folder under the root directory of the partition is called Efi,uefi will automatically go to find the corresponding boot file (. efi)

If you have just created Ubuntu (kylin)-13.04-64-bit start u disk, you can open it and you will find that the partition filesystem is FAT32 and does have an EFI folder, Go inside and see the various. EFI boot files (here again to emphasize 64-bit, 32-bit under which you cannot find this folder). So now you want to make bootable U-disk or mobile hard disk is simple, just need to copy and paste on the line.

Legacy BIOS Boot how it's started or booted.

When the system is first booted, or when the system is reset, the processor executes a code at a known location. This position is in the basic input/output system (BIOS). The CPU calls this reset vector to start a program at a known address in the Flash/rom. Typically, it performs a start 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 MBR The first sector inside . At this point the bootstrapper is loaded into RAM and executed. This boot loader is less than 512 bytes in size (one sector). After the BIOS self-test is completed, the MBR code is read into memory, the control is given to the MBR, and the MBR reads the DPT , from the DPT (Disk Partition table, the hard disk partition table occupies 6 of the MBR sector 4 bytes (offset 01beh--offset 01FDH)) identify all partitions of the hard disk which is the active primary partition. So far, all systems are the same. Here's the difference. When the DPT reads the primary partition and then finds the PBR (Partition boot record partition boot records ) for this primary partition, PBR is located in the first sector of the active primary partition. When installing different operating systems, PBR is changed, and XP's PBR writes dead code to find NTLDR. and Vista and 7 of PBR are written in to find Bootmgr.

The Boot Manager interface is not displayed on the monitor at this time. After Bootmgr was found, management was handed over to Bootmgr. Boot Manager first reads the language version information of the Boot Manager menu from the BCD and then calls the BOOTMGR with the corresponding language's BOOTMGR. Exe. MUI makes up the boot menu for the appropriate language before the boot manager is displayed on the display, which is the text interface that selects multiple operating systems. Finally, when you choose the appropriate operating system, here is Win7 or 8 (if you choose XP, will go to the XP boot process, find XP Ntldr and then start), Bootmgr to find the system partition (System partition and primary partition concept is not the same OH) windows/system3 2 under the Winload.exe load operating system kernel.

EFI Boot Introduction

EFI's full name is the Extensible Firmware Interface (extensible Firmware Interface), which is the recommended standard for Intel Corporation for new types of firmware architectures, interfaces, and services. The standard has two main uses: to provide a set of standard operating environment for the boot program of the operating system and some applications running when the computer is initialized, and to provide an interactive protocol for the operating system to communicate with the firmware.

Simply put, EFI is the replacement of the BIOS. It provides a more powerful, secure, and convenient way to interact with the operating system and firmware. The EFI specification defines the interfaces, including data tables that contain platform information, that can be used in OS Loader and OS startup and runtime services.

EFI the firmware provides several technical advantages:

Boot capability supports large capacity disks (more than 2 TIB);

Faster start-up;

The architecture of the independent CPU;

Independent drivers for the CPU;

Flexible pre-operating system environment, including network functions;

Modular design;

EFI boot also requires a special partition table that points to a special file. Typically the file is located in the \efi path, and EFI boot involves a boot loader written to firmware, EFI does not place the launcher in the MBR ,firmware knows how to read The partition table and the FAT file format. The EFI system partition is a specific partition formatted with the FAT format, which contains the boot loader, which is the EFI executable that can be loaded and run by the EFI Boot manager.

The Boot loader is set to a file that can be accessed through the firmware. The Boot loader allows the user to select and load the operating system. All boot managers include an EFI variable that is used to define the firmware configuration parameters.

MBR with GPT

MBR: Master boot record, abbreviation: MBR, also known as the boot Sector , is the first sector that the computer must read when it accesses the hard disk, and its three-dimensional address on the hard disk is (cylinder, head, sector) = (0 , 0, 1).

The main boot sector records information about the hard disk itself and the size and location of each partition of the hard disk, which is an important entry point for data information. If it is compromised, the basic data structure information on the hard disk will be lost, and it will be necessary to re-access the original data after a tedious and tentative reconstruction of the structure information. The information in the main boot sector is written through a partitioner, which is a low-level format product that has no relation to the operating system (the operating system is created on top of the advanced formatted hard disk partition and is associated with a certain file system).

For hard disks, the possible number of bytes for a sector is 128x2n (n=0,1,2,3). In most cases, take n=2, which is the size of a sector (sector) of bytes .

MBR Limitations of:

Up to 4 primary partitions or 3 primary partitions + one extended partition in the MBR partition table: The structure of the master boot record is known to contain only a single disk partition table of up to four bytes. Because each partition information requires A maximum of three bytes, it is possible to identify up to 4 primary partitions (Primary partition) for hard disks with MBR-type partition structures .

MBR Partition scheme cannot support more than 2TB capacity of the disk . Because this scheme uses 4 bytes to store the total number of sectors of the partition, the maximum can represent 2 of the number of 32 sectors, calculated per sector 512 bytes, each partition maximum can not exceed 2TB. When the disk capacity exceeds 2TB, the starting position of the partition cannot be represented.

GPT: Globally unique identity partition table (GUID Partition table, abbreviation: GPT) is the partition structure of an entity hard disk. The GUID partition table (GPT) was introduced as part of the extensible Firmware Interface (EFI) program. relative to PC commonly used older master boot record (MBR) partitioning scheme, GPT provides a more flexible disk partitioning mechanism.

GPT using GUIDs partition table (GPT) disk Partitioning system.

GPT disk provides the following benefits:

A maximum of 128 partitions are allowed, and a master boot record (MBR) disk can support 124 additional partitions within 4 primary and extended partitions.

Volume capacity greater than 2 TB is allowed, while 2 TB is the limit of MBR disks.

Because the partition table provides replication and cyclic redundancy check-in (CRC) protection, it is more reliable.

Can be used as a storage volume on all x64-based platforms, including platforms running Windows XP Professional x64 Edition. Starting with Windows Server 2003 SP1, GPT disks can also be used as storage volumes on x86-based Windows platforms.

Can be used as a boot volume on x64-based Windows 7, Windows Vista, and Windows Server 2008 editions. Starting with Windows Server 2003 SP1, GPT disks can also be used as boot volumes on Itanium-based systems.

Note: Windows supports only GPT disk booting from a system that contains Unified extensible Firmware Interface (UEFI) boot firmware.

Note: Which systems support UEFI boot? Why can't we support 32bit win8 UEFI boot at this moment?

The build of our BIOS is currently in x64 mode, so the 32-bit WIN8 UEFI is not supported.

Summary: UEFI It's a new BIOS. , Legacy is the traditional BIOS . The system you install in UEFI mode can only be booted in UEFI mode, so if you are a system installed in legacy mode, you can only enter the system in Legacy mode. UEFI only supports system and the disk partition must be GPT mode, the traditional BIOS uses INT13 interrupt to read the disk, can read only 64KB at a time , very inefficient, and UEFI can read 1MBat a time, loading faster. In addition, Win8is further optimized for UEFI support, which is known to enable instantaneous booting.

Two boot modes for UEFI and Legacy bios

Related Article

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.